Are "Buttons" Necessary for Invsalign Treatment?

Invisalign buttons are used to aid in tooth movement. Some movements can better be accomplished with these "buttons", also known as attachments. Your teeth will move with and without the attachments, but some certain movements, like rotating teeth, are move effective when using buttons. It is hard to say if the same movement can be accomplished without buttons as I have not seen your case, but most likely if Invisalign put them there, then they are needed for the fastest and most efficient treatment with the best outcome. 

I always tell my patients that if they do not want attachments, the treatment may take longer and that there may be a slight compromise in the final treatment result  (depending on the exact movement we are accomplishing.)

Some cases don't need buttons at all, and others need many.  Buttons apply forces to the teeth that otherwise won't move as desired.  While you noticed some movement, it likely wasn't as much as desired when the treating Doctor and Invisalign planned out the case.

I would say that if buttons are part of your treatment plan, then you need them.  Anything less will give a less than desired result.