In the manager settings, does the number you choose dictate how many hitters will be walked or in what situations they'll be walked?

For example, if a team has one or two stud hitters, and the rest are meh...if I set my IBB setting to 5, will that simply walk the stud hitters more often, or will it mean my pitchers start walking poor hitters as well?

it's the latter

this thread should give you an idea of what happens when you put it at 5 (it's not great!):

https://www.whatifsports.com/forums/Posts.aspx?topicID=514995

There's a quote in that thread though from crazystengel:

"As far as I can recall I only used the "5" setting once, and that was for games against a division rival in a prog league who had Babe Ruth in one of his monster seasons, surrounded in the lineup by a bunch of slugs. It worked out pretty well, too."

This is the type of situation I'm trying to figure out. Would there be an optimal setting for getting around 1 or 2 stud hitters every time? Maybe a 3 setting?