If you end up participating in subreddits that discuss political topics the mods of subreddit A will ban you for even participating in subreddit B. Or the mods or some other user on the subreddit will report you after trawling through your post history.
Now I am not fully against this. If you find a user in you subreddit who has a habit of posting opinions on some other subreddit that go on the lines of "Women should not be allowed to work and are only mean to make kids" they probably are functioning on a very different set of axioms and will probably make your space worse with their participation.
But things can get petty pretty quickly.
So you essentially end up maintaining different alts for different topics or subreddits.