I did an embroidery demo the other week for our local quilting group, but a question I was asked a lot was hoop or no hoop?
Believe it or not, I am usually hoop free for cross stitch several other types of surface embroidery. Although some types of embroidery - particularly canvas work, needlepoint, cut work and pulled work require tension, cross-stitch, blackwork and surface work don't require the tension of a hoop.
I tried it because I saw other experienced (i.e "cool") stitchers without a hoop. The benefits are 1) you don't have to keep moving the hoop for a large piece and potentially damage stitches you have laid in and 2) you don't get hoop marks which are fairly hard to iron out (and I used to get grease in mine). Another benefit is that it's easy to manipulate the fabric in terms of needle and thread placement and it's less strain on the hand.
In terms of maintaining tension, in fact, I do hold the piece I am working with somewhat taut while I am stitching on it, but it doesn't have to be as tight as with a hoop really. And I am careful to pull stitches evenly – not too hard as in pulled work and not too loose. I think that more than the tight cloth helps with tension.
There are some caveats. One is that you should wash your hands before stitching, but that's a good rule of thumb even if you are using a hoop.
The other is that you will need to iron your fabric when the piece is complete. However, what creases there are won't be as deep as with a hoop. You can mitigate this by always rolling your fabric instead of folding it.
Interestingly, when I do need hoop-style tension, I prefer something else like stretcher bars or, for extra long pieces, scroll frames. The tend to place tension to the edge of the work, reducing the need to iron and hoop marks even more.
If you like hoops and are good at managing them, then keep using them, but I do recommend to try it once without it.