Must I leave my Tesla plugged in overnight?  

It is totally up to you to decide whether or not to charge your Tesla every night.  

The Tesla battery can take being charged every night, so you can do that if you desire.  

If you want your Tesla to run at its best,  

experts recommend keeping the battery charged to between 50 and 80 percent.  

So, if it's convenient, you can charge up to 80% every night. If you don't drive your Tesla very much,

you might be able to get by with charging it once a week instead of every few days. 

it will come down to personal tastes and needs, as well as reviews and ratings from experts in the field.