The only thing you lose with a wifi only tablet might be GPS. Many android tablets include it anyway whereas only iPads with cellular service have it (regardless of whether you use the cellular)
GPS is required for some intelligent flight modes like follow me but otherwise you have full functionality.
Maps can be cached over wifi in advance or with tethered connection to your phone.
You cannot tether to your phone to access GPS though.
Flying with a tablet is hugely recommended though. I just started using an iPad
mini 2 with GPS and it makes a big difference. You can see much more.