Massive data storage streaming and backup and game servers. Disk space and CPU and bandwidth for that in the cloud would be....a lot. A lot a lot, vs a $150 rack server off EBay and a pile of used SAS drives.

Power is pretty cheap here though. All my machines run at about 150-250 watts total, that can add up if your costs are high.

Also I just like my stuff here instead of somewhere else.