Without any subscription the bot will go into a "sleeping" mode after it haven't been used in around 3-5 minutes if I remember correctly. With the Always Alive subscription it will not go into this "sleeping" mode. It will take a few extra seconds to wake up which will result in a slower response time for the first message after the 3-5 minute inactivity. This is all from memory of some previous messages from the team so don't take me up on it!