It should rely on your own comfort, and the comfort of your group, as well.

There are tanks out there who can very effectively tank entire Expert Roulette dungeons in their DPS stance, even doing massive pulls, and due to their skill, their healers don't even notice the difference. And then there are tanks out there who stay in their tank stance the entire time and only do small pulls.

Both kinds of tanks can get through their dungeons. One may take 5-10 minutes longer, but they'll still get through it.

As a tank, you have two main jobs: keep hate and survive. Everything else is secondary, and a matter of personal opinion, and group etiquette. Maximizing your DPS as a tank is a noble goal, and may make your runs faster--so long as you're still able to do your first two jobs. And with how encounters are formatted in this game, and with how tanks work, there are many ways that tanks can effectively switch into their DPS stances without sacrificing their performance as tanks.

Should you do it?

That's up to you and your group to decide.