I inboard cant the rifle in standing, unsupported. I didn't realize it until I videotaped myself during a practice session at my home range and watched the tape. I have about 5 degrees of inboard cant and after analyzing it, the reason why I instinctively do it is to fit the rifle's position to my body without having to adjust my body to the rifle. When I'm standling, I like to keep my neck and head inline with my spine and when I naturally hold the rifle after shoulding the stock, it settles in with an inboard cant.
If I try to force it to be level, I find myself thinking more about keeping the rifle level and trying to position my head and neck to allow the rifle to do so, and I find it more distracting than anything else.
Cant in general isn't a bad thing as long as your cant is consistent.
The one position where many people cant is sitting, and I actually have little to no cant in sitting, since I'm able to get pretty tight in position with the rifle without being uncomfortable (for sitting).