In my explanation of crossing a slimy rope bridge, I only required a roll if the characters move too fast or do something else while on the bridge. Other people, I know, would always call for a roll. I think the reason for this is what I referred to elsewhere as "Chekhov's Gun Syndrome".Chekhov's Gun, of course, is the dramatic principle that you shouldn't include something (like a gun) unless it's going to be used (by shooting someone with it.) It's not ironclad: you could have a tense moment in a story where someone threatens to grab the gun and shoot it, but doesn't; that still counts as "using the gun". The point is really that including a gun causes readers or audience members to expect the gun to somehow be part of the story.
In RPGs, there's a similar idea that there's no reason to include something in a situation unless it's going to matter in some way. You don't include a rope bridge unless someone can fall off that bridge. This encourages GMs to call for rolls to avoid slipping and falling. And on a meta level, having dice at the table, or skills listed on a character sheet, encourages people to roll the dice or make skill checks.
But we don't need to be rigid about it. A rope bridge can simply be there for the potential of having someone fall, for example in the middle of a fight. Or it can be there for the potential to set fire to it after crossing, to cut off pursuit. Likewise, boulders on a ledge don't mean someone is going to roll them down on you, but do mean that someone could choose to do so, or choose to hide behind them, or choose to roll them into a position to block the path. Unlike drama, RPGs focus on potential interaction with the environment.