Minor league stats are almost entirely cosmetic. Absolutely entirely cosmetic below AAA. They're fun to look at to see what kind of crazy things the sim will spit out, and that's it. The only other use I can think of is that a guy in AAA performing way better than his ratings suggest may be having a career year, if you believe in that particular theory, and could be useful as an emergency callup. I haven't observed anywhere near a large enough sample size to prove or disprove that theory, and it may be entirely impossible to do so considering emergency callups don't usually accumulate a lot of playing time. But anecdotally, it's worked for me in a pinch—for example, I had so many injuries to my pitching staff last season that I had to call up
this guy, who I selected from among other bad options based on his AAA stats, and he continued to outperform his ratings at the ML level. If you don't believe in the career year theory, then yeah, there's no use for minor league stats beyond seeing if a guy can steal 200 bases in a season or whatever.