Okay, the main reason the company gets the orrigional copy of the SM's bible: Rights Agreement
Basically, in the rights agreement for <show X> will be a section of what needs to be returned to the royalty house, and what the theatre can keep (and who gets to keep it). The standard contract has something along the lines of "All copies of the script must be returned, however a single copy may be kept by the hirer for archive purposes." There is also a section that deals with prompt copies etc. There is also the fact that any work done whilst in the employ of the company does in fact belong to the company. That means that if you want to keep the orrigional, it is by agreement with the owner of the company.
I certainly suggest you read over the rights agreement for every show you do.
Basically, the SM's who keep a copy of their bibles are often breaking the law in doing so - the company and royalty house usually turn a blind eye to that practice though.
As for giving a copy to the director - usually a really really really big no-no. Basically, you having a copy of the prompt copy is frowned upon but ignored, however if you give a copy to someone else, you go from "Possessing copyrighted material without holding the rights to it" to "Unauthorised distribution of copyrighted works". Slap on the wrist verses a couple of thousand dollar fine if the royalty house presses charges.
So from a legal standpoint - you should only have the orrigional copy of the bible if the company does not wish to keep it. If the company wishes to keep the bible, then officially, you should not have a copy.
And just a Post Script: Many royalty houses require that performance reports be sent in (some demand that they come when the scripts are returned, some do random audits) which means the company has to get them from the prompt copy. And as a PPS: Upon completion of the show, all confidential personell data (medical forms etc) should be destroyed immediatly. If you were also in charge of contracts, the company MUST keep the contracts (they often contain things like right of first refusal). I have seen 2 companies go under (that I know of) because they were sued for breach of contract because they forgot RoFR