I have some storage on a remote server that is not mine. I want to use encfs to store data there. Is encfs totally worthless if I don't dismount the folder?
Yes. If you don't unmount the folder, then the files are just as accessible as they would be on a normal file system.
If you're using the data for backup purposes, look into Duplicity, which will provide encryption while still allowing for fast transfers through binary diff'ing. If you want volume-level encryption, just use normal volume encryption on a file and unmount and copy the file.