The button is designed to absorb the flex in the arrow during shooting.
This vid shows what a button does.
http://www.youtube.com/watch?v=TmtoEjjkgEA
The button (in basic terms) straightens the arrow after the loose, and eliminates some of the effects of Archers paradox. Basically it straigthens the arrow. For you bow a button should be a must before the stabalisers. You can get buttons quite cheap. If you know some one who can help you tune the button to your setup get his help. It can take some time to tune or if you know some one who knows what they are doing it can take a matter of minuites. Alternatively , I am pretty sure, there are plenty of posts and topics explaining button tuning. Just do a search.