I check it when I am flying far distances and am dealing with weather or conditions that could change. Also if I am board and just doing my PIC due diligence.
The last time I really was paying attention to it there was a large cell moving east bound and I was coming from the southwest and wanted to make sure I was staying ahead of it. Along with in cockpit NEXRAD and talking to flight watch I listened to HIWAS. It was one, but not the only, tool I used.