I used to be a loyal chess piece. Frankly, it got boring. I switch around now. My squad +++Heathen Nation+++ does now. No set time, rhyme or reason. Just do what feels good to capture the style of game play I'm looking for.
The only side switcher I despise is the player that is working with you when you're playing to win the map as you build up more players, then suddenly, switch to attack 5 sets of NOE bombers. Your bombers. It's like, "jeez. You switched to bump your score". I know. It's just a cartoon game. But it's weasely and disrespectful.
Short of trying to pad your stats playing cheap, I encourage switching. Ive always been treated right on each country. Haven't met many players I didn't like.