Some people love to watch
TV but who once start online streaming it is rare he/she will again addicted to TV and streaming uses lot of GB. Higher quality streaming uses huge GBs. Some people use SD resolution streaming (I also) but there are times when HD streaming required specially some instruction videos with lot of text.
Online games use lot of GB.
Video chatting uses lot of GB
Live video streaming uses lot of GB
Etc.
And there are times download also needed for
Windows update, Linux Update etc.. New software installing, occasionally other files etc.
But a normal user usually dont do all the mentioned thing with equal quantity.
But a normal user usually do some the the mentioned thing.