Although the question has already been answered, I would like to give my opinion, based on AMP development and deploying experience.
You have to do data/document backup on a regular basis, but you must do backup before installing AMP.
Some nodes properties can be added/removed/modified more than once especially during early AMP development stage. This can likely lead to Alfresco not starting up or some node being gone or unusable forever. I remember a plugin tutorial from Jeff Pott, mentioning a conservative (start with few properties, add later if needed rather than removing) approach when developing AMP, because a simple removed property could cause huge problems.
So...a backup before installing AMP is strongly recommended.