for me, i just search for the biggest files in my devices, then dedupe the ones with same file-size. Then I take a look on thumbnails of the big files and dedupe in case the thumbnails are the same (^but the file-size is not). Then I sort all the left files on size and look out for general data of same file-size and then decide whether to delete without breaking things or just leave them.

but, I'm thinking putting a NAS in my home and do all the neccessary backup onto that.