Star Citizen

I have used multiple accounts simultaneously for a few purposes. Mostly with another computer, but more recently with a SteamDeck.

Usually I have my alt setup as a getaway driver, especially if I'm running some FPS mission in a PvP hotspot. I usually have a Nursa setup for respawning, but if I have some bad luck (and run out of med gel) I can always have my alt blitz to my main's body for a quick revival. There's also the option of having a literal getaway driver if I decide I want to have some fun breaking out of prison.

Pro tip: if hacking away your CS, have the account with CS go to Kareah first, then have your alt pickup the "Kareah Infiltrated" mission, so that they can land safely and then revive your CS character in the case where you get overrun. Alternatively, you can start the hacking process, then go hide somewhere safe while your alt completes the hack for you.

They can also be useful for "hot drops" near comm arrays (line the ship up right, go full speed and hop out with my main just as I'm passing the array). Then pick up the ECN alert "Network Intrusion Detected" once the comm array hack has begun. This allows you to park the ship immediately outside of the comm array for a faster getaway.

Note: Years ago, picking up this mission with an alt had the side effect of preventing other players from being able to accept this contract. This would effectively allow you to hack the comm array without having to worry about interference. You could even accept the mission to bring a comm array back online and just ignore it to keep an array offline for as long as you wanted. Luckily they eventually patched it out (now, multiple players can accept the same contract for protecting comm arrays).

I have occasionally used my alt for mining in an argo mole. It works pretty well. I have also used it for manning the torpedo launchers on the Polaris, as well as the EMP on the Antares.

If you set up something like an Xbox controller to connect to the other device, it makes it a lot easier to have the alt push whatever button you need without having to completely switch between screens (as well as the occasional input needed to keep the client from timing out due to inactivity).

You could also revive a soft deathed ship and just have your alt fly the other ship back to a hangar instead of having to ditch your main ship.

I haven't done it personally (yet), but for something like the player marketplace it can help to have an alt that's ready to sell something to other players at a moment's notice. My alt could already be at their home location, waiting for the buyer to arrive. Meanwhile, I can mostly continue what I'm already doing with my main without having to pack up early and miss out on some loot/contract completion.