What is a floating-point locale? I define it as a location which you the GM have created, but that doesn't have a particular location in your game world. When creating content for a Homebrew world, I like to put together a handful of settlements and interesting places (The Screaming Cliffs, The Spell-Shaper Sands, The Village of Arns'Borough, etc). These places have stories, and encounters, maybe they tie together in a quest. The point of having them floating is to not tie yourself to a decision you may later regret.
The Tradition Model
Not to say that this is a bad style, but I have seen GM's build together a massive world with every city on the map and dungeon complexes riddling the hills. The problem arises when the GM has a plan and a story, but needs the players to travel to a certain town. If the players want to go somewhere else however, this can turn into railroading, and quickly sap the fun from the game.
What if you want your players to run into the Tall Tower of Terror, but they took a left turn instead of a right at the Stinking Swamp? Easy, just reposition the tower to be somewhere else. It only exists in a place once you describe it there, a little like Schroedinger's Dungeon.
My favorite style for this is with towns. Creating all the NPC's necessary to populate a town that sticks in the players memory can be time consuming, and you want them to experience it. So create that town, but don't set it down into a location until the players are ready to find a good resting spot between adventures, then you can bust out the Dwarven Blacksmith and Tiefling Merchant you've been practicing. Making the world exist around the players might not fit into every campaign, but it is a usefull trick up your sleeve.
So what are the downsides?
Well, the biggest one is cohesion, does your world make sense? This method of location placement can lead to some strange situations if not handled properly or abused. "You mean Dracula's Castle showed up in Saudi Arabia?" Like any technique, this hinges on the GM to make everything work right, and it shouldn't come at the expense of your players or story. It is simply another tool for that toolbox.