As I've said in previous postings, there's this thing called a dispositional question. It's an epiphanic question of the type you'd only think to ask if you're disposed to question everything.
These questions are often agrammatic and weird looking. Often they have a kind of caveman syntax: "Why girls liking important?," "Why is cool good?," "Why does height mean desired?," and such.
So, here's one in that format: "Why penis is good?"
Take a second to try and answer. It turns out to be a hard one (so starts an unfortunate set of amazing puns). There are going to be four sets of guys, here: ones that have no idea (is that you? if so, you probably care about size, etc.), ones that don't care, ones that think it doesn't matter, and ones that know the answer. I'm pretending to be in that last category, but I'm open to being wrong.
The answer necessarily involves a discussion of another dispositional question, "What are vaginas?" Take a second to try to answer that one, too.
Here's a first-pass answer.
They're different from penises in some ways, and like them in others. Like penises, vaginas can be aroused. They can be stimulated to create orgasmic contractions. They produce lubrication (yes, penises do this, too.) Finally, they can be stimulated to produce a stream of fluids (so-called squirting. yes, it's a real phenomenon. google "skeens gland.") Importantly, vaginas are also capable of translating the so-called ninth sense, "stretch," as a pleasurable moment. Vaginal canals and labias have different shapes and sizes. And vaginas, again like penises, are stimulated by BOTH sensory and psychological inputs.
Unlike penises, vaginas can orgasm without being touched (penises can, too, but it's not a thing that's proximate to seduction).
Unlike penises, and in order of importance, here's how vaginas differ from penises: there's a second orgasmic organ called the clitoris that sits right outside the vagina. Vaginal arousal is "non-obvious," both to observers and to the woman herself (note that we describe vaginas as "dripping" instead of as "hard," even though both signify arousal). Vaginas hold stress tension, like upper backs, for instance. (Vaginal "knots" feel like rice grains, not like egg-sized lumps, btw.) Vaginas are acidic environments. Vaginas menstruate. Vaginas and penises both have a "hedonic geometry," but they're different. Finally, vaginas can get yeast infections with much greater frequency than penises.
Now, back to the question, why is penis good?
The vaginal canal is not dumb tissue. The vaginal entrance has different textures and nervous sensitivities than the vaginal canal contains closer to the cervix. The floor and the roof are proximate to different tissues: the floor abuts the nervous anal passage, the roof pushes against the spongey musculature surrounding the bladder, and the sides communicate with the long nerves of the legs.
With the hand, you can stimulate each region to create arousal, massage each region to allow the inflow of blood, and vibrate (really: palpitate) each region toward climax.
So why is the penis good?
The short answer is: for orgasm, it's not.
The plunger-shaped head pulls competitor's sperm out of the vaginal passage. It has the ability to cause orgasm, which inducts sperm into the ovaries with greater efficacy.'And it gets sperm closer to the ovaries. But, for the woman's pleasure--at least her orgasmic pleasure, it is less physically efficacious than either hands or (if you know what you're doing) words.
There isn't much left for the penis to do. She'll cum better manually, and the candlelight in your apt will relax her toward orgasm better than your penis ever will. So what is it good for?
As far as you go, it's your limbic center. Awesome. Is that also what it is for her?
Yes.
Your penis represents your desire for pleasure. She can use it to tame you, to tease you, or to impress you. She can also use it to pleasure herself, but most often, it's the bounce or grind of the clitoris against your pubic bone that triggers her climax.
What are the implications of this?
(1) size doesn't matter. You causing her to cum is largely not a feature of your dick size. Indeed, an understanding of feminine anatomy puts a smaller, smarter partner categorically beyond a larger,, dumber guy. (2) size is subservient to longevity. The biggest issue women have is a lack of arousing foreplay prior to sex. (3) the penis occurs to men as a physical instrument, and to women as a psychological instrument. Let it be. Use angles and lighting to make it seem bigger, if you want. If you're smaller, be more aggressive during oral. Cause it to take up psychological space , and don't worry about how many actual square inches it has. A smaller, dominant penis is more valuable than a larger, subservient one any day of the week.
There's lots of things here that I've hinted at without fully explicating, but I'm more interested in what folks think than putting a pin in any subpoint. I want this thread to be about "what a penis is good for." If you have other questions, ask away , and I'll start a new thread to address them.