Reasons for movers:
No dimmers
Easier toubleshooting, one immediately knows the problem is either
DMX addressing or the moving light itself.
Easier cable runs. Running
DMX, even if it takes several universes for that many movers, is considerably easier than several load-rated cables.
Moving lights accept changes considerably easier, positioning, focusing, color, and
gobo selections can all happen without getting on a lift or the
truss.
Perhaps
CMY color mixing is used, not a color wheel
Reasons for pars:
Their
color temperature is generally better for cameras
Easier to hang, I certainly would perfer hanging a
par to hanging a mover
Less expensive
Far less fragile
Easy to repair, fixing moving lights can be a nightmare from what I've heard, though some fixes are pretty easy for movers too.
Less
DMX channels (a good or bad reason depending on the
console in control)
There are a few ideas for each.