I've never replaced traditional guides from a factory rod but I do build all my own rods with micros. With correct placement of micros, you would actually use more guides. As an example a traditional 7' factory built spinning rod, there would likely be around 7 guides total. A well built custom rod with micros would have 8-11(ish) guides. All depends on the handle placement, reel used and guides used.
To convert a factory rod to a good micro set up, it would be very probable that all guides would need to be removed and most, if not all, replaced with different sizes and style.
The advantage of micros is solely weight reduction. Reducing weight on (especially) the top 1/2 of the rod greatly changes felt weight and action of the blank itself. Unless you have an older rod (15+yrs) with a good blank built with a traditional guide set up, I'm not sure it is worth the effort. Most decent newer factory rods have some version of a micro guide set up. The newer factory rods that don't have some kind of micro guide set up, are going to be so low in quality to start with that spending the money and time, would not be worth the minimal gain on those rods.