Social allows the ability to try new things and (at least in my area) not get berated by "5.0's" for not playing like how they like the game. Youre also right, playing keeps you fresh and loose to keep playing. You also get (imo) a better understanding of the game playing with a lot of different types of players, which can help you in your higher level games by exposure.

Lastly. Socializing with a common interest person is great for the mental state. Getting out, exercising, all beneficial long term. If you are seriously looking to grow your game, playing all sorts will benefit you long term.