I flew 8 months of FPV without OSD (and still don't have it on my Phantom).
But, once I added it to my f450, wow, what an added sense of security it offers.
Most of the telemetry I disregard (tho neat to look at sometimes), but being able to see the battery voltage is _priceless_, because otherwise theres no practical way to know that than using a timer.
It also tells you how many satellites it's getting, and shows you distance from home, .so you know that it's recorded a proper home location.