My personal stuff is about 12-15000 rolls of 35, 1000+ 120 and a couple of 100 4x5. Some years ago I went through my files and shredded any left over stuff that was shot for clients. Before that I had given some clients the original negs/skidees, just to make some space. Over the decades I must I have shot 30 000+ rolls of 35, probably 2-3000 rolls of 120 and a lot of 4x5/8x10. Most everything is filed in ClearVue pages and binders - tagged by year/month and with marks on the file pages as to what has been scanned or printed. Not perfect file system - but it works in a fashion.
Of course there are about 80 Carousel trays (140) with chromes - as well as a big box with several 100 file sheets with assorted slides. Now and then I am gripped by a "sorting" frenzy and go through these and shred some.
I find that Flickr helps - when I scan and upload I tag the image and if needed I can find the original negative/slide. Of course, not everything is good, most is mundane but somehow it holds some interest (to me at least) - and as time goes by - the images takes on a historical interest. Things change fast and a shot from only 15-20 years ago can be more interesting just because changes.
Of course, moving between countries and continents has taken its toll. A box of negative binders from the early 60's is forever lost. Which is too bad as negatives/slides also work as mnemonics - looking at them can put you back to a place and emotion.