This is pretty common for me. In the studio when I want faster recycle times I may bump the ISO up a stop or two. On location I'm often trying to balance flash with dim ambient light, so the ISO is already pretty high.
I agree with Bennett with the idea that in the studio recycle rate is king and increasing the ISO is a way to increase that based on lower flash output. A suggestion is to test with your ISO in your studio with the flash to see the differing results ie. see where the sweet spot is for your camera with the ISO and flash recycle rate. As a rule of thumb always learn and ISO and leave it low to limit any noise and artifacting which i'm quite sure you already know. The beauty of Studios is that you have the control and usually the time.
Strobist photography is great and a lot of fun.