I have used it as a backing fabric and it came out nice. There are lots of different weights of microfiber. Most micro fiber is on the heavy side and I would have concerns about mixing the weight with a lighter cotton.
I did not use it in piecing the top as its poly and really does not like to crease , and I like to really get my blocks flat. Combining it with cotton can be a problem and the poly will melt at the temperature you normally would use to press cotton.