Allá tú is used to communicate that you don’t necessarily agree with the decision someone is making and that you are excusing yourself from any responsibility for the consequences. Here are some examples:
- Allá tú. It’s your life. Do what you want. It’s up to you.
- Allá tú Fine. Leave me out of it. Es muy tu bronca.
- Allá tú. Suit yourself. As you wish. Como quieras.
- Allá tú. If you do that, it’s on you. I’m not backing you up.
El más allá is the great beyond, where we presumably go after death.
Recall that allá is a variant of allí, just as acá is a variant of aquí.