Well the main reasons I did that is with Win7 forward, alot of the data of games (I have nearly a TB from Steam) is default dumped to Documents, even updates and install files it needs to go back to in a few cases (I hate Origin / EA!!!). Further the 'cache' directories for programs don't default to temp like back in XP, so they all are under your C:\Users\Username\AppData\Local and then Roaming , like when I am on Second Life, or downloading patches, and so on... so much stuff gets 'dumped' under your profile since 7 was released now.
I discovered that by still using Steffen Gerlach's 2002 Drive Scanner program and seeing in pie chart then 'digging down' and watching how much is used in each directory. I was quite surprised how things are 'delivered' to my computer. For example Good Ole Games (GOG.COM) when you buy games only downloads and sources the download (when the game looks for where it needs source files) under your Local folder under a GOG folder. Was really shocked how things were dumped under profile directories these days.