Allot of my work is free handed right onto the body and my reasons are simple, body symmetry and individual musculature. Getting any design to fit and looking like it belongs there is important to me, a tattoo is an enhancement and should accentuate and compliment it's placement. It's also much easier for me to draw it to size right on the client and give them a preview of what I plan to do. Most of my free-hand pieces are not planned out in the usual sense either, I usually ask for nothing more than a concept when the appointment is made, then either draw it out of my head or do some research for source material images. Many times I get a visual when people describe what they'd like and I usually go with my first instinct, but often visualize several different ideas, I'm usually thinking 'outside of the box'.
When I refer to freehanding a design 'out of my head', it simply means that I had no source material in front of me but worked from memory. I don't need a picture of a Cross to draw one, a Wolf , Skull or Rose either. I've drawn and studied so many images over the years and have stored so many in my head that allot of times I can just conjure images up on the spot, it's just what I do...
This is one of the things that I enjoy most since I love drawing so much. Most of my Animal pieces are free-handed as is all my Floral work, and occasionally, even some Celtic knot-work.
Naturally 'photo-realistic' work can be free handed, but requires a photo, this isn't done from memory. I do on occasion have clients that insist I free hand a portrait, they wind up paying for the drawing time.