One of the things that annoyed the shit out of me when I was on Reddit is when users would sift through the post/comment history of your account to use as ammunition in an argument they are having with you now. Is there a way to block or limit access to my account history?
And then you get banned if you (even accidentally) upvote something with two accounts.
That requires the host instance to have set up proper anti alt measures, or the admins of the instance with the upvoted post to be paying close attention. As such I am pretty sure with only 2 accounts the chances of detection are minimal.