First and formost, if you are a human at max charisma you should need to put additional mana into a bind just about never. The only time to consider it would be if you failed your second binding attemp and your circle was weakened on both (it is possiblek to fail and they don't try to attack you rarely).
If you play an arial, svirf, gnome, dark elf thats when you actually need to use mana on your bind.
The mana put into the bind ONLY affects landing the bind spell succesfully. It will in no way shape or form affect how the servitor acts once it is bound.
You can choose to play ultra catious and always use lots of mana in the bind but you are kicking yourself in the ass. To be successful as a conjurer (in a PvP sense) it is all about balancing your timers. Those extra hours you spend regening mana can make it more difficult to do so (especially if you are a human and generally your pets come fairly happy)
