In reality, Friday was mostly spent recuperating from the week and they didn't do any more of what they wanted to do.

This was exactly my experience when I worked a M-Th 4x10 shift. Tired every day from the long day so I wouldn't do anything during the week and then just crash Thursday night, sleep in Friday, start getting productive in the afternoon.

Also, very important, depending on where you live it's highly unlikely that that '10' hour work day includes your lunches, so you're actually at work for 11-12 hours every day.

That said, the absolute best shift I've ever had was a 4x10, but it wasn't four days in a row:

Work Monday & Tuesday, Wednesday off, work Thursday & Friday, Saturday & Sunday off.

Knowing that you're never more than two days from a day off is something fuckin special.

This shift meant I didn't burn out during the week and had a bonus day mid-week to take care of errands and whatnot.

However, this was base-level helpdesk work. There is no way in hell I'd want to try and work 10 hour shifts while being a sysadmin primarily focused on project work. There is definite diminishing returns when you're working a job that requires real thought.