lightning requires having something online all the time. so there's no real turning it off if you wanna use it.
Discussion
Well the only time I use it is when I pull it off exchanges, but maybe nodes will close the channels if I am offline for too long?
absolutely. plus when turning it on, before it can be used, it needs to download the new understanding of the graih from its peers. similar to downloading the new blocks that you missed while your Bitcoin node was offline.
lastly, it's a security risk. if you don't turn it on at least every two weeks (by default) then someone could close the channel you have with them using an old state, potentially stealing your funds.