I only use a strobe when I need to.
Recently I had a gig to shoot 5K/10K foot race. There was hardly any light in early morning rain (90 mins after sunrise) so the strobe (at low power) was required to produce a decent image of the runners in motion. Even when the rain stopped and there was a bit more light, I used the strobe at until the sun came out. Much later that day I shot a short kids race on a very shady street. I used the strobe then as well.
There were ~ 1,500 people in this event. Sometimes I had to take a photo every few seconds. Using a quality strobe (SB-800) with 2700 mAh AAs) at low power got the job done.
For interior shots such as birthday parties, I like to use the strobe off camera. I usually place it high in the corner of the room so the light bounces around and fire it remotely using Pocket Wizards.
It is possible to produce a photograph where the strobe light only augments the existing light. I hate photographs where the strobe dominates the light to produce that nuked-out look.
I also very much enjoy using available light. But when the light's not right, or when people are moving around, subtle use of strobes can produce rewarding results.
