Apple ID Merging

Hello,

I am in the process of setting up a new phone and moving from a relative’s Apple ID- apparently when I sign out it will give me the chance to merge my purchases? I was wondering when they say ‘merge’, what actually gets merged and what might I be charged for- I don’t want to carry over app and music purchases from 5 years ago as it isn’t helpful, but merging the apps I use (mostly free) would help in terms of updates.

Any advice would be appreciated

😊