Two reasons I would have:
- My link has a fancy schmancy color-changing digital display that shows you the pressure at a glance on the actual robot.
- AD showed me them in person at champs last year and I was impressed.
We've been using that Rev one though on robots recently. Giving drivers & pit crew a dial with the pressure is, at least in my mind, very useful for seeing why something doesn't work as expected
Again though, this presumes unlimited resources. If you're on a budget, a good-old analog dial will do just fine.