why do some sportsbooks let you adjust your parlay selections at checkout

makes sense from a convenience angle i guess. like, say you get to the end, you double-check, and realize you want to switch out a team, or maybe swap an over for an under. it keeps you in their system longer too, less likely you rage-quit the bet if you can tweak it on the fly. feels a little like those last-minute numbers switches i see at the roulette table - half gut, half paranoia. but then i start thinking, does that really give an edge to the player or are they just making you second-guess yourself, maybe change a better pick for a worse one after you already built the ticket? do you actually take advantage of the feature, or does it just trip you up?