It's worth mentioning that the Par for the course is what's used to work out your handicap adjustments at an amateur level.
E.g. If the par for the course is 72 and I have a hcap of 10 and I shoot 80, I'm net 70 and therefore 2 under my handicap. This would result in a handicap cut.
If I shoot 88, I'm net 78 and 6 over par and would get a handicap increase.
In a professional context, comparing scores to par for the overall course will give you an idea of how easy the course is playing. If people are shooting low 60's then the course is generally playing easy and if they are shooting mid 70's then it is likely playing hard.
In both amateur and professional situations comparing vs par for each hole is useful for a number of reasons such as.
Competitions can work out which holes have the lowest score and highest score vs par, meaning they can rank the holes for difficulty across all competitors vs a common base level.
Exceptional scores can be noted, a 2 on a par 4 is exceptional, whereas a 2 on a par 3 is usually not as exceptional.
(This also works the other way, where in an amateur context exceptionally high scores may be discarded to avoid an increase if its felt that was a one off.)
In stableford competitions par can be used to work out when you no longer score, meaning that things can be sped up. If my handicap doesn't allow me a shot on a par 3 and I've already taken 5 shots then there isn't any point me taking a 6th from a scoring perspective.