I'd rather watch movies, read, play certain games, etc. on my tablet than on a phone. (Obviously there are also specific use cases like digital art.) That said, I mostly use my tablet when traveling and it's a distant third in necessity compared to either a laptop or a phone--and only somewhat more useful than a smartwatch.
Watching movies on a tablet is terrible, though. All methods for propping the device up so you can watch the movie are inferior to the way a laptop screen props itself up via hinges and a base.
On a plane I'd rather use the tablet in my lap than have to put the tray table down. And in a hotel room I'm watching on the couch if there is one. (I do also have an attachment for my tablet that will let you prop it up on a table but I mostly don't use it because it adds weight.)
For reading, I'm probably bringing my Kindle along if I don't bring my tablet.
