Making capsules serves two purposes for me.
First, it's like a sieve. Everything filters through the grid of the capsule guidelines you're working with--there are many (color capsules, function capsules, season capsules, personality capsules as someone just suggested, tiny and wide-ranging capsules, predictable and bold capsules) and we get to make the rules up for ourselves if we want.
In the end of a capsule exercise I find out which functional needs are met, unmet, or over-saturated, and the same for relationships (color, proportion, style) that make things work as a wardrobe or stand out as orphans or single-use items. I know where to purge and what to add. I always have new ideas about how things might work together. It's always a little head-smacking for me.
If I never use the capsules as defined units, just hang it all back up and get dressed as usual, my wardrobe and dressing are automatically smarter for the exercise.
Second, of course, is for travel, which I do a lot. I don't have travel capsules per se, but having build my wardrobe around a few color-based capsules it's much easier to choose and mix things around to suit what I need and want for the next trip. Before capsules I would flail around for hours and still not get the packing right.