I'm using other accounts I own, while launching the second one on the same profile selected, a warning appears telling that could cause issues with saves and otherwise.
I'm using Magic Launcher, using the same profile, no issues at all. I'm on multiplayer servers all time so the single player shouldn't be affect me.
The warning should appear when you run it for the first time, or an option to enable/disable warnings (experimental) because I need to play with 2 accounts for administrative purposes on my server.
And, every time I start the launcher from another computer/location, I need to retype my password on my main computer, that is annoying to retype every time, unlike MagicLauncher that does save, when you launch, it authenticates the user. Why the launcher doesn't do that instead keeping the token... I liked the old gen launchers, also missing commandlines from shortcuts (Sorry offtopic)
Use the -workDir option