This spell honestly has me scratching my head with the way it's worded.
Astral Projection states the following:
If you enter a new plane or return to the plane you were on when casting this spell, your body and possessions are transported along the silver cord, allowing you to re-enter your body as you enter the new plane.
As this is worded, can I remain in my astral body if I so choose?
To clarify the uses, let me list some potential applications derived from this:
If your material body and astral body remain apart upon entering a plane other than the Astral Plane, you could:
1. Have a Gore-free clone:
Use the astral body as a gore-free multi-creature version of the Spell clone that has all astral copies of the gear you had when casting Astral Projection. You can stash your real body in a secret, hard to find location (kind of like a phylactery for a lich, only it's your own body) The only "telling" factor is the 1-foot Tether between your shoulders pointing to your body like a compass. You can "safely" run into danger fully knowing your tether to your material body is exclusively located on the plane you are on. When you die you return to where you hid your body. Best case scenario nobody managed to find or rob your "bunker". Ideally you (and your associates) have amassed a stash of material components to simply cast Astral Projection all over and weasel your way back onto the plane, doing the hiding thing all over again and running back into danger. A long-term plan with lots of bumps (like finding your way through the astral plane to the same portal over and over), but this would work for some BBEG-ish type.
2. Become Practically Immortal:
Keep in mind: Mental health is not factored into this example.
While Astral Projection is in effect your material body stops aging, decaying requiring sustenance, even air. While you walk the earth within your astral body you still require anything your mortal form does and age according to the rules of the plane you're on (agelessness is strictly linked to your material body and the Astral Plane). You can live out a full life in your astral body; even die of old age and you would snap back into your up to then time-locked body, the mind of an old man inside a young body. Assuming the caster has a life expectancy of 50-ish years from when Astral Projection was first cast (and he prepares a new set of components for every future casting of the ritual) the caster could - assuming he wakes up in his true body and immediately begins casting the spell again - live up to 438000 lives (as many hours as there are in 50 years), meaning he could theoretically live 17 520 000 years altogether. And that doesn't even factor in the potential of supplying his material body with a few Potions of Longevity (which have an upper limit of de-aging uses, but still hold the chance of de-aging him 9 times for an average(from 1d6+6, 4+6 = 10) of 90 years).
3. Escape from a "BRING HIM TO ME, ALIVE" situation.
Stuck in a bad bind? Does some powerful bad person want you or something stuck in your head? Not a problem if you are currently using your astral body and put your real body away safely. Just kill yourself. Your soul will return to your real, unharmed (and potentially younger, differently groomed body and the people after you will tear their hair out since Locate Creature only goes out for a mile. If your astral body aged significantly / you changed your clothes, hair, etc. they're also going to have a damn hard time recognizing your true self (or your new astral body after casting Astral Projection yet again). Infinite hijinks.
4. Have an "evil" twin
Assume your best friend died. Sad. Further assume he escaped the afterlife to haunt you. Amazing. Just give your material body to your ghost pal.(A minor stretch). A ghost can possess your material body without any resistance (due to your suspended animation your material body is functionally incapacitated, thus failing any checks automatically. Your material body's perfectly operable as per the description of a ghost's possession feature, it exclusively affects your body, puppeteering your muscles. Admittedly, now you rely on your already once-killed friend not getting you killed, but that's what you got yourself into by keeping them around anyway.