No reason to keep either on since they drain the battery even when not actively browsing the net. And if your LTE can’t find a tower to connect, it keeps trying to connect, draining the battery significantly. This was pretty bad for me a couple years ago; not so much anymore since I live in a city now but I still keep both off, mostly habit but also because I like having my battery above 90% while it’s sitting idle.

When I’m at home and want to use the net on my phone, I turn WiFi on, then off once done. When I’m outside the home and need the internet, I turn LTE on and then turn it back off once I’m done.