The more people who run a full node, the greater the decentralization[1][2].
I can't run a full node full time right now because there is no upload throttling. The Bitcoin client slows my Internet down to literally unusable (4sec+ pings).
Not because of hard drive space. I've got 900 GB free right now.
What kind of Internet connection do you have? I'm running a full node on a refurb low end Mac mini...I can't tell that I'm running it...I do have a 100mbit/s connection, but I think I would do fine with 1/10 that.