Mike may be right. I may be an idiot and it probably shouldn't take anyone 10 minutes to adjust a line-up, but I need 3-5 minutes to look up stats and make decisions, another couple of minutes to physically enter the changes and then another 3-5 minutes to scratch my head and figure out why the line-up wouldn't save.
He's also right that the injury scenario is weak since it only occurs, at worst, a few times a year, but the others happen with fair regularity.
I'd be all for dropping the DH/no-DH line-ups (speaking of "grossly underused features") which, until I actually have interleague games, I set to recommendations just to keep WIS from telling me I have incomplete line-ups.
And while I'm agreeing with everyone, I'll agree with tecwrg that few people would want to maintain 8 different line-ups, which is where the "save line-ups" or "recall line-ups" feature would come in. It's "copy and paste" and not "multiple line-ups," so it's work you've already done, just work you don't have to re-do.
And even if I get good at this game someday and I learn to adjust a line-up in under 5 minutes, 5 minutes is still 5 minutes and we spend a lot of money in RL to save 5 minutes here and there, e.g., toasters, garage door openers, remote controls, velcro fasteners and last-but-not-least the Slap-Chop®.