It all depends on the target, how far, and how fast. I shoot IDPA and USPSA competition every week, and the best iron-sight shooters are looking at the target under almost all conditions, unless it's a tight shot at 15+ yards.
I agree with RickB, but with a caveat: when shooting IDPA/USPSA, I'm now looking at the target,
through my sights. Much different than looking at the target and being oblivious to and unaware of the sights.
For action-type shooting, though, I "only" need to hit an area roughly equivalent to an 8". Hardly target accuracy. But I need to do it fast and after transitioning to & from targets and positions. The sights aren't irrelevant, but I don't need crisp resolution to get 8" accuracy, either. What I
do need to do is "see" what's out there. So I look at the target
through the sights. IOW, I see a
specific point on the target I want to hit (just "seeing" a big tan piece of cardboard is much too vague), while being acutely aware of the sights.
For precision work, such as target and group shooting, though, it's all about perfectly-aligned sights, in which case it's imperative get a good crisp focus on the front sight. And in IDPA/USPSA, the longer and tighter the shot has to be, then, the more I come back to the front sight.
I recently started shooting IDPA (& even more recently, USPSA), and, ironically, struggle with accuracy issues. A top shooter recently pointed out this "look at the target through the sights" approach". I'm finding it tough to let go of a front sight focus when action shooting, but I've been practicing it a bunch lately, and it's becoming easier, and hits are getting better. I can still shoot a very respectable 15 yard group, though, and I do it by laser focus on the front sight.