Consistent self-voting i.e voting your own posts without upvoting quality content of others is definitely frowned upon in Hive.  This can be in the form of you using an account with minimal stake for posting only and using another account with high stake for upvoting mainly your own content only.  It being frowned upon doesn't mean it is not allowed but it would certainly create a bad impression of the self-voter as it implies that the self-voter is here to 'take only' but not to 'give'.

Some users have more than one account to represent different interests. For instance, someone interested in Sports and Finance may have an account for Sports (with stakes in Sports tokens) and another account for Finance (with stakes in Leo tokens). Personally I find it difficult to say it is inappropriate in such cases for one account to upvote the other account or vice versa. 

A third scenario is when you follow a curation trail and if the account you are following upvotes your post, your post automatically gets a "self-vote". In such a scenario, the self-vote is not an intentional act on your part and cannot and should not be faulted.