It depends what bike I am riding. Every now and then I will ride my fancy crabon bikecycle, and will have opportunities to beat some strava PRs. But those were also set on that bike, so when I ride my usual commuter (has to weigh close on 40 lbs with everything loaded up), I tend to take it easier. I generally ride how I feel. If I feel like putting in a burst of speed, I do it. If I feel like rolling an easy 14 mph, I do that. Most of the time I will save my "sprints" for the sketchier parts of my commute where I have to get in traffic to make a left turn, or for the road that has no shoulder and heavy traffic.