It does tend to increase the visible grain, so until now I've used it only with low-speed film. On 35mm you'd use it with fast film only if you're looking for a gritty, high-contrast look. But with larger negatives the grain becomes correspondingly smaller. So I recently tried using medium format Delta 400 with Rodinal. The results are really quite good:
This looks great to me. Both the highlights and shadows retain detail even in a high-contrast scene like this. And at full resolution (about 25Mp in this case), where the scanner is already losing image detail, the grain is noticeable, but not at all intrusive:
Here's another image from the same roll:
I like this look a lot. Sharp and clear, without excessive contrast. I'm certainly going to use this combination more in the future. Might even try it in 35mm, just to see what it's like, though I suspect it gets a little grainy for my taste.