Standstills

I don't get it.  What is the basis for an agreement where an investor agrees to limit future share purchases in exchange for representation on the board of directors?  Is it a bad thing for someone to acquire a large block?  Even if it is, isn't there a conflict of interest in the group making the deal (the current board, I assume).  In fact, can a board even strike a binding agreement on who will be on the board of directors?  Perhaps votes are such a fiction that nomination (perhaps this can be agreed) are sufficient?  I'm really very confused by the conflicts and the message.