I view it primarily as just another pleasurable sensation the dominant can give to the submissive -- as a reward, special occasion or simply because he wants to. I happen to enjoy it, so "never" wouldn't be an option, because then I'd be depriving myself of something I enjoy doing.

In talking with female dominants with male submissives about this, though -- admittedly years ago, so outlooks might have changed -- it was common for it to be viewed as a submissive act, so was less common in that context (<listening to all the male submissives screaming "you fucking bastard!">).

But I'm not sure I agree with that (<listening to all the male submissives heaving a sigh of relief>">) -- because aside from any aspects of submissiveness, it also puts the dominants teeth in contact with some sensitive bits that can be used to reinforce the dominant aspect -- emphatically, if deemed necessary (<listening to all the male submissives screaming "you fucking bastard!">).