While this rule obviously does benefit the bigger clubs the most, most decisions that are made across the board do. Bigger clubs are in better position to take advantage of almost all rule changes. Unless a rule is specifically made to benefit "smaller" clubs, like parachute payments, then that's just the fact of the matter realistically.
In terms of affects, there are loads; and while it enables big clubs to make the most of their squad depth, it also helps the smaller clubs rest their players and protect the fitness of their players (where they have a lower number of quality players and need to stretch them out across more games).
If they're 4-0 down with 20 minutes to go, you could probably take your best players off and let them get some rest before the next game and not risk losing the next game before it starts.
During games it gives more flexibility in terms of tactics to big clubs and allows them to flex their bench, but in games in "big" against "small" teams, if the disparity is as big as people suggest, then it's not really a change of result on average (from winning to losing), but just likely means the bigger teams win bigger.
There are a load more benefits of course, but over the course of the next season, the smaller clubs will also benefit from using their subs and not running their smaller squads into the ground through overplaying in futile situations.
I'm not sure I'd say it "sucks" for the smaller clubs, but they definitely benefit less than the bigger clubs like us - or City with their mega squad.
