Advantages are that it forces you to keep steem power (which could turn out to be a good thing), and maybe it could also affect how people perceive your account. If you're 100% power up all the time, maybe people see you as a long-term player and would want to support more. But that's just perception. Nowadays it may be better to do 50% / 50% for a variety of reasons.

No best time to post really! I publish anytime. But if you want to try, observe american timing. Publish something in their morning/afternoons :)