From my understanding of the format it seems to accept any custom attributes with keyed data, i have used the plugin to save some of my facial rig curves ( collection of expressions such as Smile, Jaw Open ranging from 0 - 1.0 ) so i can easily swap them between rigs, in terms of space switching i guess the problem is, that you have to know exactly what you want to save/load :/. Handling unique rig controls can be a bit tricky,
Its best to use it with generalized controls ( biped ) incase you want to make sure the atom clips will load between different rigs correctly ( still no retargeting hehe ). I just started using it a few months ago but so far i have not ran into issues or scary things. The flexiblity of a anim library that is not a maya scene has def some cool advantages.