You would only lose access to music not saved in an accessible location (and purchased after DRM was removed unless you took the steps to get drm free tracks[1]) and also software bought on the App Store.

[1]funny story: I have one (or more) tracks in my music library that a friend shared with me almost 20 years ago when we were in college and he added me as one of the 5 computers that could play the tracks. Every time I’ve moved my library to a new computer it asks me to log into that account to approve that track, but it won’t give me a list of the tracks so I can delete it/them. It isn’t enough of an annoyance that I’ve tried too hard to find them.