ToME: the Tales of Maj'Eyal

How exactly do I use this new parameter?

And, more to the point, what does it do? Does it allow me to set where ToME stores the profiles and savegames?

And yes it means it'll look for your profile,settings,saves,... in that folder
If you are on windows, the launcher may get a visual feature to define it in a few days

Perfect.

I was wondering how to specify drive letter etc.

I'll just wait for the new launcher. Great job on that one, by the way!