What does sperm do to vaginas?

I read on Twitter we shouldn’t have men ejaculate into our vaginas constantly but it didn’t say why. My new partner has a vasectomy, so I won’t get pregnant and we’ve both been tested so good there. I’m wondering if I should let him cum in me or if it will throw my ph off and my cooter will smell bad? Any women with similar experiences? Or know what sperm does to vaginas? Any advice helps