Almost immediately after my dry suit class, I began realizing that using the BC for bouyancy and the suit for squeeze is a lot more comfortable. The biggest problem in using the suit for bouyancy for me is the extra volume of air in my legs....kicking becomes much more tiring. I try to maintain a very slightly heads-up position to compensate for this, but it still is a problem.
Always adjust the drysuit for comfort FIRST, then go and adjust your BC. That way you aren't playing the balancing game.
In certain situations I would use my suit for primary bouyancy however. Take my dive on monday night...I was carrying the flag in my left hand, my flashlight in my right. Now, my left hand had to deal with venting my BC, grabbing my computer, and adjusting the flag. My right hand dealt with inflating my suit, using the light, and doing any of the other assorted tasks that might be required. I was definately task loaded, as I am new to night diving (but it is darn cool!). In retrospect, I think I would have felt much more comfy if I had just used my suit for bouyancy, as a simple raise of the arm would have been enough to vent on the way up.
Now, I started drysuit diving the day I started my certification courses, so in the beginning it was benificial to use oonly the suit for bouyancy as it was much less complicated. Then I moved on to adjusting both.