Michael mentioned the integration with the dust extractor. The cost of the 2 is quite shocking for doing the 2 things most of all of us dislike - sanding and vacuuming. However, the Festool ETS EC 150/5 paired with a Festool Midi (built-in blue tooth which is wonderful with that little push button adder - not required for the corded sander but still worth mentioning) is something that I'd pay for again without a doubt!
As Jim mentioned, the mesh sandpaper (with backer) makes the dust extraction a "breeze".
I know you weren't asking about a the dust extraction but that combo really is quite surprisingly a game changer.