You think it doesn’t? It can build up after a while! 
I currently have one client, and I’ve been working on 5 trees (1 for me, 2 for friends, and 2 for the Daughters of the American Revolution). The DAR and Daughters of the Confederacy registrars have also been using me as a sort of go-to-gal for documents that they’re having trouble finding, or for transcriptions (10 years of reading physician handwriting have paid off).
In the last month, I have downloaded 846 photo files and scanned documents, 76 pdf’s, 22 Word documents (four of them were books of 100+ pages). When you save a photo or media file to Family Tree Maker, you end up with at least 6 copies of it (the one I saved to my hard drive, the one on the current tree, and the 4 backups I made throughout the month). I know better on the backups – ultimately, they get stored in an encrypted folder on the cloud drive, with only the most recent on my laptop – but I got really lazy on the original ones that I saved to add to FTM, and hadn’t cleaned out my temp folder this month.
All told, when I cleaned out my genealogy storage this afternoon, and emptied my Recycle Bin, it was 12.6 gig of data. And I’m not even a full time genealogist.
My computer is not even a year old, so I don’t have any appreciable increase in speed from my monthly cleaning, but anyone with an older computer should take note and clean out your files every once in a while. I think I will move my schedule up to every two weeks, while I’m in the busy season.
Genealogy Addict 