IMO, open carry removes a ton of tactical advantage. If the puke in the convenient store is gonna rob the place, the last thing I want him to know is that I am carrying, until I am ready for him to know.
There is heated debate about this, and I know alot of people feel open carry gives up no tactical advantage, and that is fine for them. For me, I want every ounce of advantage I can get. The few times my oc would change a pukes plans, vs the tactical advantage I loose is not a good trade to me.
A hostage situation is EXTREMELY rare, but does happen. The tactical advantage to cc is obvious.
The bad guy knows he is gonna do something bad before you know he is, so if he sees your open carry and carries through with his plans, you are toast.