yes there is a difference in using a hoop vs without. However, both are acceptable and show good results.
Using a hoop or fram gends to be a bit more flatter than without. However both are ok if get the results you want.
A large quilt tends to become cumbersome if quilting without a hoop or frame.
I really prefer the No Slip Hoop - can get them at JoAnns. Largest is 14" which works for all sizes. It is about $20.
But, when set in hoop it does not slip. I use it in all my classes and even seasoned quilters rave about it.
I can never get the quilt to be the tightness/looseness I want with the Q-Snap.

First of all don't change what works for you.....in other words...if you have been quilting without a frame or hoop and enjoy it, forget what you read to change your method. I don't use a hoop or frame either and that is the way I'll always quilt from now on. I tried hoops and a frame and hated it. Now one thing I have noticed from reading this thread is the "bunching up the quilt in your hands when handquilting without a frame or hoop? My quilts are smooth on my lap or table and I have one hand on top and one hand underneath moving along the quilt not only to guide the needle but to feel to make sure that there are no wrinkles happening on the bottom. That's the way I do it anyway.

Bottom line, don't change what you enjoy just because someone says there is a better way. It doesn't hurt to try something new but I wouldn't drive myself crazy trying to get it right either , JMHO.

It really takes practice. I personally wouldn't quilt without a hoop or frame. It would be helpful for you to sit down WITH A HAND QUILTER and watch her/him, and then have her/him watch you and guide you along. Try visiting the hand quilting writers at http://celebratehandquilting.blogspot.com and see what you can get from that group. They are pretty knowledgeable!