The relatively high cost of our interrupt makes us an unlikely candidate for interrupt duty. However, it's nice to have the option if your raid comp is light on interrupters. I'm not called to interrupt due to the combination of high cost and signifigant impact on my DPS rotation, but I like being able to backup someone in a pinch.
The excuse I'm used to hearing on this part is "I don't care about your DPS, just interrupt even if you have chance to miss" since we put about 2-3 interrupts / cycle just incase someone misses/chokes. I find my self either pooling energy too much or having to use TF to interupt instead of dps