For those of us that enjoy using rayon, we do so because we find it imparts the least amount of taste of any wicking medium. For a lot of rayon users they find they can suddenly taste their resistance wire over their wicking medium, as apposed to the taste of the wick masking the taste of the wire. Of course everyone's tastes are different.
Also, where a lot of people go wrong with using rayon is they use similar amounts as they would with cotton. Cotton expands once wet, rayon shrinks slightly when wet(it also takes on a rigid texture and holds in place much better.) Sometimes rayon may shrink in the coil hours after you wicked it, which can lead to sudden dry hits because part of the coil isn't touching the wick anymore.
There is a very fine line between too much rayon and not enough, even more so than there is with cotton IMO. Once you nail consistency though, rayon has it's own set of awesome attributes. For me I can go up to 15 watts higher, or take longer drags at same wattage, with rayon using the exact same coil as I would with cotton, it just wicks that much better/faster for me, YMMV.
I still love my cotton, but my rayon/cellucotton is that much better. Add temp control into the mix and I will be in vaping heaven. Let's not forget squonking either (added in to keep on subject slightly)