The answer is: Really fucking important.
The Blues are 9-2-2 this season when Roman Polak is in the lineup. When Tyson Strachan is in the lineup the Blues are 9-8-2. So, the Blues average 1.54 points per game when Polak is around, which would come to 126 points over a whole season. With Strachan those numbers are 1.05 and 86.
Now, of course, not everything else is equal here. So, this isn't a slap at Tyson. But clearly this team plays better when Roman is healthy.