In the micro, nothing. We'd have a bunch of extra cash we can spend on other stuff.
In the macro?
The overall goal is keeping the US competitive in technology. Both in terms of producing/controlling IP as well as (perhaps even more crucially) remaining a premier destination for technologists from all over the world. The cost of not achieving that goal is... incalculable, but large.
Whether or not this is a good way to achieve that goal is of course up for debate.
It's not just the economic cost that is a consideration here. The military applications of AI are potentially staggering (as are the associated ethical concerns - but, as with any military tech, once someone does it and the advantages become clear, others will inevitably follow). No major power player is going to want to risk getting drastically outpaced by its primary competitors.
Note that this isn't a hypothetical, either. Israel is already using AI to pick targets. Ukraine is already using AI-controlled drones to beat jamming. There's no indication that either one intends to stop anytime soon, which tells the others that the tech is working for this purpose.
