Tyranitar, Abomasnow, and Hippowdon are all slower than Politoed, so if your opponent has those, it's best to keep Politoed in reserve. Otherwise, the slower weather starter will win the weather war, and Politoed would have to switch out and back in (switching in general is usually risky in doubles) or resort to having a Rain Dance user bring back the rain.
If your opponent doesn't have one of those weather starters, then not usually, but I'm sure there are reasonable circumstances depending on the team it's being used on and is up against.