A lot of paladins will say throw in a Shield Swipe here and there to save TP on long fights. That's true to an extent - you can do similar though with slipping Flash into your single target rotations more. Paladins have very low TP costs compared to pretty much every other class, so as said, you really should be running out of TP -last-, but it's still a minor reason for Shield Swipe. If the fight is long and you have a threat lead, try and use it here and there.

It does have other uses though. It's slightly more damage-per-GCD than the Halone Combo too (Halone combo averages 203 potency per GCD, Shield Swipe is 210) so if you have a decent threat lead and want to contribute to DPS more, you'll do a little more damage by using Shield Swipe as often as possible over just spamming Halone.

Also, it -can- be a good thing to use on trash mobs for damage reduction. Yes, a 6 second stun is better but both stuns and pacifications have diminishing returns. If you're pulling a big pack of mobs and you know most have nasty melee abilities, tabbing to off-targets to throw alternately stuns-then-swipes can certainly help... though in today's day of mass pulling speed runs chances are that you can't really afford to do that without threat issues. It's still a viable skill to weave.

But in general... you could likely remove shield swipe from your bars and only see a tiny loss in effectiveness. It has its uses, but they're situational.