For all of my waterproof / breathable outerwear, I'll wash once at the beginning of the season, once at the end, and sometimes another one or two times mid-season if I notice the DWR failing more often than normal or I sweat a lot in a given piece.
Contrary to popular belief, washing & drying waterproof / breathable laminates helps a ton when you do it right. When you sweat in your gear all those oils can get into the membrane and DWR and decrease both weather resistance and breathability. This is why I tend to wash my touring outerwear more often than my resort outerwear.
If you want a very detailed, nerdy summary of why & how to wash technical outerwear, this article
is worth a read.