Dropbox/ contains stuff that I’ll need when I’m away from home.

Downloads/ gets purged every few years of stale downloads.

Documents/ gets mission-critical stuff that needs to be backed up but does not need to be in the cloud.

Pictures/ has all my non-Photos photos, including a quarter terabyte of DSLR raw files.

Photos and iTunes put their stuff wherever they do.

I have files from 1999 in my home directory so I’m not sure I can offer any advice on tidying up :)