When you have over 5500 episodes of television, roughly 26,000 songs at 320kbps, a few hundred DVD rips, a few hundred raw Blu-Ray rips and a couple hundred decent quality (10+ Mbps) Blu-Ray rips, space becomes an issue. I am still ripping discs and sourcing quality backup copies for my online licenses, so I'm expecting to add another thousand movies or so to the 900 I already have (note that I own legitimate copies of nearly all the movies on my server in one form or another).
A typical 1080p Blu-Ray remux (no added compression or transcoding) with lossless audio runs anywhere from 14-35 Mbps and takes up anywhere from 15-50GB. A top notch DVD rip runs around 4-5GB. TV episodes run anywhere from 2-7GB, but average 3-4GB for 1080p with DD5.1.