This is an all inclusive question for both men and women, straight and gay.
For the women, when you cum, how different is it to squeeze down on something inside your vagina as opposed to not having anything inside at all? Likewise for the guys, how different is it when you cum without that squeeze clenching around your cock vs. having a loose grasp (or even hands free)?
Usually, especially when I masturbate, at the moment I orgasm, I squeeze from my base to the head, loosen and readjust my grip, squeeze from the base to the head, and repeat until I'm done ejaculating. Sort of like squeezing an almost empty tube of toothpaste.
Obviously, this is to aid the PC muscles in ejecting the semen from the cock. When ejaculating into a vagina, unless she's cumming simultaneously, the squeeze/release/squeeze/release cycle is more from the engorgement spasms coupled with the tight ring around the entroitus. Probably why guys try reaching so deep inside at the moment of discharge. In an evolutionary sense, not only to try getting the semen as deep as possible, but re-create the stroking sensation when masturbating.
Let me try elaborating that last sentence. When I ejaculate, the first spurt is instinctively when I shove it in as deep as possible and flex my PC muscle. This is when my cock is the most rigid, the most engorged. As soon as the first "rope" is out, my cock reverts back to its normal rigid state, I relax the kegel and I slightly withdraw. Her introitus acting as a tight ring around my base slides up my shaft, creating that tube of toothpaste/pulling the semen out squeeze from base to head I was describing earlier. That point when I'm shallowest, I kegel and shove it back in as deep as possible, discharging more semen.
There are other times when I kegel/relax/kegel/relax when I'm fully extended inside her, but the clenching sensation is still there from the engorgement within her vaginal walls.
The only time I've ever not squeezed my cock when I ejaculated was when I was experimenting with male multiple orgasms. I rubbed myself until that point where I'd do the "squeeze the toothpaste out" motion, but instead of clenching my fist around my cock, I let go and simply let my dick take care of the rest. It was less fulfilling. A lot less. So much so that I did maintain a slight erection and I could get back into a full blown erection in a few minutes (as opposed to my usual hour or two refractory period).
So, you're turn.