Timing straps?

When modding your extracted BIOS rom file, how do you know which timing straps to copy where (ie. take 1500 and paste into 2000 mhz)? I'm trying to wrap my head around WHY we're doing that? Why can't I take 2000 and paste it everywhere?

Apologies if it sounds dumb, I'm not a pro at this and just trying to learn.
Thank you!