It all depends on how the micros are done and cared for.
To me, micros are really skinny braids. But there's two ways to get skinny braids. You can use less extension hair on a not-so-small section of your hair so the resulting braid is skinny. Or you can take two hairs of your own and attach a good size of extension hair to make a skinny braid. So in the first instance (
red being extension hair and black your hair), each braid is made up of
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And in the second scenario:
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The resulting braid is of the same size, but the second scenario shows a lot of extension hair per section of your own, which means it exerts a lot more extra weight on your hair and scalp. THAT is the type of micro that is a disaster waiting to happen.
After you get micros, maintenance is important. Your head is carrying more hair than it's used to so that in itself is quite a feat. But then if you're pulling your hair back all the time, you further exert strain on your hairline. And when you have some growth or the extension hair moves away from your scalp due to sliding so that the braid is dangling instead of being firmly rooted at your scalp, that's an accident waiting to happen. Your first warning is the braids swing painfully. This is particularly true along your hairline, so that MUST be redone...as soon as the braids get loose.
I sometimes take the extensions out and just wear my own hair in twists as bangs to give my hairline a break. Or I may cornrow my own hair back a bit to give the same effect you'd get if you wore a headband and pushed your hair back.
To close, I'll use a picture that was on another topic but that shows you how much extension hair I use per braid section and you can see the resulting braid is truly skinny, but it's not being held to my scalp by two hairs:
Also notice in the above braids, you can see the base of the braid (the square that was parted) because the sections are much bigger than the resulting braid since less extension hair than the section is used.
Now below are the micros that can cause damage:
Notice you can't really see the real hair at the base of the braids because very little hair is used per extension hair so it's completely buried by the larger amount of extension hair. That would exert too much strain on the scalp and a tug could easily lead to traction alopecia.