My wife and I have grandfathered verizon unlimited data plans on each of our phones. We use one of them as a mobile hotspot when camping, along with a sleek booster and external antenna.
Despite the fact that we have 'unlimited' data plans, the mobile hotspot feature is not unlimited. It's $20 per month for 2GB and I think $20 for 1 GB after you go over the original 2GB limit. We turn it on when we depart on a trip and turn it off when we get home.
We don't usually turn the hotspot off at night.
We spent last week camped at the beach and I was reviewing usage on the verizon website each day just out of curiosity. I noticed that something was using small amounts of data every few minutes all night long and throughout the early morning hours. I turn my laptop off at night (usually around 10pm), but my wife's Ipad is not turned off, it goes to sleep mode. I think her Ipad is checking email every few minutes. Next time we will try turning off the Ipad as well.