When you create your locations using the Location Information window, you can indicate that a location contains inventoried items that shouldn't be entered on a sale. You'll do this by marking the option Items cannot be sold or shipped from this location in the window. When you mark this option, the location won't appear on the Select from List window for sales.
You might want to use this option if you have a repair location, for example. You'll want to move items into the repair location, but you don't want to sell from there; you'll want to move them out of the repair location and into the selling location. (To add a location for inventoried items or To edit a location for inventoried items)