It adds a determinate structure. I don't know, as a player, that the GM is going to be satisfied with 3 checks, or if he might decide to require 20, or what they will be on, their DCs, nothing. At least as a player, in the process of dealing with this challenge, I can reason about each part. "Oh, we don't have any failures so far, and we have 2 successes already? OK, maybe the hard DC Religion check by the cleric to convince the guard we're Baal worshipers is not so dire a thing." At 2 fails, maybe we start to think about backing out! This is a game, it has game considerations, but also saying "yeah, we got our 4th success, GM we are through!" is actually a big deal.