I know this has been brought up before, and the problems people had with it were:
1) It doesn't work with escalating cards.
2) It will take too long to play.
3) LOL, that's dumb, I'd never play it!
Basically, the idea is to limit the number of armies to 12 per territory.
It's not meant to be played with escalating cards.
The game is more aggressive than others that get bogged down by over-building, and as far as I can tell, will be faster than standard fixed/no card games.
The attacks can't take more than 12 rolls to resolve, and almost always fewer. Although this point doesn't make a difference if you auto-attack, I like to see how my attacks go so I don't end up dropping to three and leaving my opponent with more.
Most importantly, I've been playing this way for ages, with modified fixed sets, and it works really well. The games are balanced, rely more on strategy and don't take all day to play.
If you don't want to play it, I wouldn't be bothered. There are plenty of escalating set games where you can put 200 armies on the Ukraine and stream roll everyone left. This option would be for players who want more strategy in the game.
If anyone's wondering, and maybe you'll like this idea better than 12/place, the modified fixed set gives 4 for mixed and 6, 8, 10 for the others. Since the mixed set is most common, giving it the least amount makes the game less luck-dependent.