Permanent rain is one of the most game-changing elements in Pokémon and therefore Politoed is going to be used a lot. Actually I could write only about Drizzle in this post rather than Politoed, because the ability is more important than the Pokémon itself. But Politoed isn't horrible either, it could be literally worse.
The effects of rain, just for recollection:
(copy - paste from here:
http://www.smogon.com/dp/articles/rain_offense)
- The power of Water-type moves is boosted by 50%.
- The power of Fire-type moves is reduced by 50%.
- The move Thunder has 100% accuracy and can hit through Protect and Detect 30% of the time. Note that this only occurs in Diamond and Pearl versions - Protect always blocks Thunder even in the rain in Pokémon Platinum, Pokémon Battle Revolution, and Pokemon HeartGold and SoulSilver.
- The move SolarBeam has a base power of 60.
- The move Weather Ball becomes the Water-type and has a base power of 100.
- The moves Moonlight, Morning Sun, and Synthesis heal only 25% of the users full health.
- Pokémon with the ability Dry Skin heal 12.5% of their max HP every turn.
- Pokémon with the Forecast ability change their type to Water.
- Pokémon with the Hydration ability heal themselves of status effects at the end of every turn.
- Pokémon with the Rain Dish ability heal 6.25% of their max HP every turn.
- Pokémon with the Swift Swim ability double their Speed.
Basically all RD Pokémon get a free Agility boost (+2) and a boost to their water STAB in rain (+1). That's insane. Quite a lot RD sweepers can outspeed common scarfers in rain while having atk/spa boosting natures and hit hard with their water STAB. Yeah, the only thing you have to do is switching Politoed once into the battle, it doesn't have to be useful, it just has to stay one turn into battle and after that it can just die / or better switch out.
Everyone who played rain dance teams (tbh rain dance teams are bad they just sweep every team that isn't prepared to rain. It doesn't matter whether the player is bad or good) know the advantages that instant rain has over Rain Dance with Damp Rock.
First of all, you don't have to use three Damp Rock users to set-up rain, but that is marginal. More important is the fact that you don't have only eight turns to abuse rain at a stretch. You can remove the weakness from steels to Fire, make Heatran useless, abuse Thunder, Rain Dish and Hydration. You can waste your turns by having a Pokémon in your team that help to deal with common weaknesses in rain teams and go on. You basically don't have to worry about rain ending.
Now to Politoed:
Politoed is for sure not the best Pokémon stat and move pool wise, but it's stat spread is far from bad and it has some good move options. I think you can give Politoed different roles depending on the style of team you are planning to use Politoed.
RD teams:
This team is focused on abusing rain (usually on the hyper offense) and you need to have constant rain. Therefore your most important member is Politoed who you have to be sure to not die before your opponent's Ninetales/Hippo/Ttar/Abomasnow are dead. It's important to eliminate/trap your opponent's weather changers etc.
A defensive set (Hypnosis / Encore / Boiling Water / filler) seems to be reasonable or an offensive that can kill your most common switch-ins (Specs Politoed (w/ Hydro Pump / Focus Blast / Ice Beam / HP whatever is important)). You really want to play this Pokémon conservative to not lose it early.
Weather control teams:
Controling weather seems to be the main focus on the early B/W metagame especially with instant weather starters to offensive weather (rain, sun) like Ninetales and Politoed probably starting in OU and the fact that you can call sand also an offensive weather now.
Many teams will rely on a specific weather their team is built around. Weather control teams with multiple instant weather changers (Politoed, Ttar and maybe Abomasnow) can easily control the current weather and beating heavy reliant weather teams while also being able to abuse it without being to addicted to a specific weather.
Politoed can be played more risky on such teams and abuse it's not that bad base 90 SpA and boosted water STAB and spam Hyro Pumps or Surfs happily. It can still run a support set that can easily be a little bit offensive oriented.
Btw guys. Caterpie with Drizzle would be still amazing and probably game-breaking. It's about instant rain, not about Politoed.
-0²