It shouldn't do any harm to use without a tripod collar, or Canon would have supplied one as standard, eg Canon 70-200/4 doesn't come with a tripod collar, but the much heavier f/2.8 version does. Canon should be ashamed of this policy, especially as they then charge a three-figure sum for a tripod collar that costs only a few quid to make, but that's another question. It's the same with lens hoods, though at least with an L lens you get one of those.
However, it's certainly good practise to use a collar with a heavy-ish lens like that, and it will make life a lot easier. The collar puts the lens/camera in good balance and without any weight pulling the camera forward, accurate framing is easier. Also, rotating the collar for vertical shots is a far better method than flipping the tripod head over 90 degrees.