Game consoles such as PS4/XB1/PS3 will auto update games even with the system in standby and those updates can be huge so there's that to think about. The biggest culprits of huge chunks of data being used would probably be digital game downloads and the patches, then there's movies wether you are downlaoding or streaming, Netflix, Youtube etc. Also make sure nobody is using your wifi somehow like a neighbor, make sure it's secured in the router with WPA2 and a password that's not easily guessable. I will say though that nowadays it's pretty easy to hit over 1TB/mo, I know because I do it and I'll be cancelling our TV service soon so we can afford our overage charges due to them implementing that in a month or 2. They need to increase the cap to 2TB minimum at least for the highest 2 speed tiers, 1TB isn't near enough. Consider when a new XB1 game comes out and say it's 70GB download, I have 2 XB1's in my house so it'll download twice, 140GB in 1 day, that's a huge chunk of the monthly allotment. This gets even worse during xmas time when tons of games come out and I usually will get up to 10 new games the last couple months of the year so can't wait to see how much I go over then.