Though I don't practice using Abhidhamma for meditation but using simple method in the Thai Forest Tradition, one thing that I completely agree with Abhidhamma in practice is that one citta does indeed arise one at a time. However, in term of practice, to try have sati to see citta arising and falling may not be the way, perhaps not possible to force one to develop sati in such a way. It comes when it comes (and it goes when it goes, can't hold on to that state, ... unless one can develop bhavana to such a high stage), i.e. one sees one citta arise and fall one at a time when the time is right, naturally. And seeing that, one also knows that it is simply impossible for more than one citta to arise at a given mind moment.
Citta arising and falling away ...on and on...is not just a mere concept. It can be observed in practice, and is fundamental as it directly demonstrates the Trai Lak nature of samsara.
But is it really important to consider individual citta in our experience/ practice? Like is it a "must"? Perhaps not.
