XOR is the appropriate operation if you're using a stream cipher to generate an arbitrarily long keystream. Or a one-time pad. It also makes random access a lot simpler.
Of course, you do actually need to generate that keystream and not just repeat a short key.
There are very few cases where you should be doing encryption without authentication... and as soon as you're doing authentication you'll be doing more than just xoring with a stream cipher output. :)
Of course, you do actually need to generate that keystream and not just repeat a short key.