The question is always asked "I have a hoop, why would I use a tapestry frame?"
Hoops are excellent if you are stitching a tablecloth, pillow cases, afghan, etc but the problem with using a hoop when stitching a picture, whether it is large or small, is that your hand that is holding the hoop can get strained and your other arm and shoulder gets sore from working the needle from the front to the back and vis versa. Tapestry frames hold your fabric taunt and both hands can work - the dominant one at the back and the other at the front. This also eliminates round marks and if you work with the tapestry rods rolled the front way rather than back then your project will also keeps cleaner as the front is rolled inside the rods.