The Master Password is the backup password for FileVault. Why would you want to remove it? You don't necessarily need to set one, but if you activate FileVault and forget your login password, the MasterPassword is the only way to access the data encrypted by FileVault.
Figure it makes more sense in a network environment where a user (employee) forgets his/her password and needs the admin (IT guy) to reset it.
I want to remove it as I cannot encrypt my account area; Filevault returns an error saying "cannot create encrypted disk image" although there is plenty of disk space.
BTW : I have posted another note about this FileVault problem