Why do my Invisalign trays have bumps on the back of them? Is this for buttons/attachments?

I just got my Invisalign aligners and after getting all the needed attachments for the front of my teeth I noticed that there were bumps on the back of my aligners. Does that mean that there should be attachments there too? My orthodontist didn't mention anything about it so I was wondering what the bumps were there for if I never ended up getting attachments there? I want to get the best result from wearing the Invisalign but if I don't have all the possible attachments how will I achieve that?