if you want to have cards on the watch, you must have a passcode.
you shouldn't have to log in "everytime you want to do something" you should only have to enter the passcode when you first put the watch on. It should stay logged in until you take it off. wearing the watch too loose, or having clothing that goes between your wrist and the watch, may make the watch think it's been taken off (I'm not sure how dark wrist tattoos will affect this). There are also settings to have the phone unlock the watch. If I forget to put in the passcode on the watch when I put it on, The next time I unlock the phone with faceID, it pops up a "unlocking watch" dialog.
you also won't have to enter the passcode every time you want to use an Apple Pay card. It will make you tap the button, but that's only so people can't just bring a reader near your wrist and charge you.
With express transit on the watch , you won't even have to press a button, I just go up to the turnstile and tap my watch on the reader and keep going. Without express transit, you have to double tap the button, then you can tap the watch on the turnstile. Express transit will still work for some time after your watch or phone has shut down due to low battery.