There's a lot of good info in this thread. Some of it is here, some of it is there. So I typed up my thoughts about micro-bevels and why to use them or not to use them. All of this is just my opinion. Others may agree or disagree. Here goes.
MICROBEVELS, my thoughts
Fact 1: The thinner the blade the better a knife will cut.
Fact 2: The lower the edge bevel angle the better the knife will cut because lower angles result in a thinner blade edge.
Fact 3: The blade needs to be thick enough to hold up to the work it is intended for.
Fact 4: The edge bevel angle needs to be high enough to reduce chipping, rolling, flattening or anything that results in a dull edge.
So there is a middle of the road that is best for any given knife depending on its use. Example: You wouldnt use a straight razor to cut fire wood and you wouldnt use an ax to shave with. These cutting tasks Id say fall at the outsides of the road. For an EDC pocket knife you need something between the razor and ax.
I have two reasons to use a micro-bevel instead of one bevel. First, lets talk about the size of the bevel(s) on a knife edge. Lets say you sharpen a knife with one bevel until it is sharp. Then you raise the angle and put another bevel on the edge apex. The first, larger bevel well call the back-bevel. The bevel at the edge apex I call a micro-bevel when its small enough that its hard to see. If the bevel on the edge apex (cutting edge) is easily seen I like to call an edge-bevel. I like to distinguish between the two bevels based on size because of the benefits or reasons to use them.
1. MICRO-BEVEL: I use a micro-bevel only as a finishing step to ensure there isnt a burr and as a very fast touch up. The angle is higher and as a rule of thumb a higher angle will decrease cutting performance. But with such a tiny micro-bevel it wont decrease cutting performance enough to notice in my opinion.
2. EDGE-BEVEL: A wider bevel at the cutting edge will strengthen the edge apex against chipping, rolling, etc. The wider bevel will decrease cutting performance more but not nearly as much as it would if the entire edge were at this higher angle. Actually, in my opinion for an EDC pocket knife neither the micro-bevel or larger edge-bevel will decrease cutting performance enough to notice.
So the reasons I use a micro-bevel are to quickly touch up an edge at a higher angle than the main bevel or primary bevel or whatever you call it. Different people use different terms for these bevels as well as the entire blade grind. The other reason Id use a different angle on the edge apex is to strengthen the steel right at the cutting edge and the lower angle back-bevel thins the blade which increases cutting performance. Since (IMO) cutting performance isnt reduced enough to notice I see not reason NOT TO USE a micro-bevel. It will strengthen the edge apex a bit and also make touch ups easier and faster.
SHARPENING METHODS and how they affect using micro-bevels (sharpening system or free hand)
Sharpening system: Using a system that you set the angle with allows two separate, accurate, flat bevels at different angles. Ive used systems before and I like to keep a record of the angles on each knife so when performing a touch up I can set the angle for the micro (edge)-bevel to what I set the sharpener to the last time I sharpened the knife. Personally, I thing the edge or micro-bevel should be 3-5 degrees higher per side for it to make any significant difference in edge strength. If you want to use a higher angle on the apex only to ensure you are hitting the apex with the stone or for a very quick touch up just one angle higher is enough. To do this however you will need to have recorded your micro-bevel angle for that knife or use a marker to re-set the sharpening system to the same angle.
Free hand: When free hand sharpening its impossible to create completely flat, accurate bevels due to human inconsistency. Therefore all bevels will be slightly convex. The edge bevel angle at the edge apex will always be higher than the angle at the top of the bevel. Therefore the apex is by nature stronger than it would be if the bevel were flat at the same angle as the top of the bevel. But if you want the angle at the apex even higher you can intentionally raise the angle a little more. Just a little practice and putting a micro-bevel on a knife free hand is quite easy.
Im sharpening free hand right now and havent used a system in a couple of years probably. Since I dont have a way to set an exact angle or have two separate flat bevels I touch up the edge by feeling when the edge apex makes contact with the stone. When a convex bevel is sliding along the stone it feels very smooth with no or very little resistance. Ill slowly raise the blade spine until I feel the apex make contact. There is a sudden increase in resistance to the sliding motion along the stone. Once I feel this I do my best to keep the angle the same and not increase the angle any. The end result is usually what appears to be one consistent bevel. In reality however (this is how I look at it) the edge bevel is higher than the rest of the bevel.
NOTE ON FREE HAND ACCURACY AND HITTING THE APEX: Since I (no one) is 100% accurate throughout one complete stroke when we try to hit the apex with 100% accuracy we will go too high as often as going too low. Therefore to ensure I dont increase the edge or micro-bevel angle any higher than I want I repeat strokes trying to err on the side of too low of an angle. My inaccuracy will still ensure I hit the apex enough to put a hair whittling edge on the knife. This theory is something I understand (I think) but it is also something you cant get the feel of overnight. Even when we do have the feel for this we are still not 100% accurate. When using a sharpening system you dont need to feel for hitting the apex. What you do need to feel for is the amount of pressure which also is essential when trying to achieve the super-sharp levels.
Again, all of this is just my opinion. As I learn more and get more experience my opinion often change.