Que de leche la vaca, y aunque respingue.

So long as the cow gives milk, it matters not if it complains and bucks.

The end justifies the means.  This seems to be the operative dogma when water boarding terrorists, or trying to get to first base.

Mejor llegar a tiempo que ser invitado

It is better to arrive on time than to be invited.

This is the mantra of everyone in my family. You invite one, and he shows up with toda la familia, all 12 of them. Early. If you arrive late, you might miss the shrimp ceviche, or the one six pack of Negro Modelo that Tio Bob brought. Besides, there are never enough chairs. It is hard to look chingon with your culo enveloping a green plastic kid chair. Trust me.

No es lo mismo atras que en ancas.

To be behind a horse is not the same as riding behind the saddle.  A bit obvious if not archaic reference to who rides and who slogs through horse shit and contemplates the horse's ass. In a  more contemporary context:  There is a BIG difference between riding shotgun and riding in the back seat.