I was at a play party a ways back, and they were sealing people into a latex vacuum cube. This is a big cube that looks like this (your head sticks out) and seals to your body, cutting off all movement. All movement; once the air is pumped out, you're not wiggling your toes without the cube's say-so. And it says "nope!"
So it's a fairly intimidating thing. And when people asked me if I wanted to get into the cube, I was nervous.
But in BDSM-land, you can negotiate. It's not "get in the cube and come what may, you're taking it." I trusted the people there more than that, or I wouldn't have been playing at all. So I said: I just wanted to feel what it was like in the cube. I did not want to be hit, groped, rolled around, or otherwise messed with while I was in there. And I got in and they pumped the air out. I felt what it was like--interesting, frankly kinda creepy--and they let the air back in and let me out.
In other words: because I could say "no" to the things I didn't want, and trust that "no" would be respected, I felt safe saying "yes" to something fairly wacky. If I hadn't been able to set limits on the experience, I wouldn't have been having the experience at all. If I sounded like Little Miss Prissy saying "not this, not that, none of that kind of fun either," I wasn't all that prissy when the end result was me getting sealed into a freaking latex vacuum cube.
I do this for regular sex, too. If I can say that no, we're not raw-dogging it; no, you're not sneaking it up my ass; no, you really have to stop when I say stop; then I can say "yes" to the sex itself. Limits may feel all limity, but within those limits, some fucking hot sex can happen. Without limits, you're not allowed in my house, much less my vagina.
You can have sex without explicit limits, but there's a catch: it has to be extremely predictable generic sex. If you have totally culturally "normal" sex--man initiates, manual, oral, then genital, orgasm and go to sleep--then there are some limits built in. But the instant you go outside that norm in any way, you make your partner worry how else you might go outside the norm. If you can't talk about that, it means that everything "weird" is off the table automatically, because enforcing total "normalcy" is your only way of ensuring they don't suddenly come at you with a greased pineapple. It's only possible to break the generic-sex script when you can explicitly say to each other, "we're going to do some weird stuff, but we agree, no pineapples."
Consent isn't just about the right to say no to everything. Sometimes it is, and that's part of it; I had every right to not go in the cube at all. But sometimes it's about saying the no's that make yes possible.