Bots will use the boosts to get instantly into TBC content and farm massive amounts of resources and gold, getting to skip all the time and expenses they’d otherwise have to spend getting there.
Because it’s instant, they can get right into the content they want to farm rather than having to level through the old zones where they might be detected and reported before doing any harm.
Profession alts (which is what all my boosts will be used for) are going to flood the economy with resources that are supposed to relatively rare due to a cooldown attached to them. Profession alts that most people wouldn’t have because leveling serves as a deterrent.