It means that if there's a launch failure, you can't just let the stuff sit there. They clearly can pump it out -- the normal sequence for this sort of test (which SpaceX generally does before every launch) involves filling the tanks and then running the engines for only a second or two, and they also obviously need procedures for last-minute launch scrubs, which can happen for a whole bunch of reasons. (One launch was recently delayed because someone steered their boat into the no-go area.)

The main operational consequence to date has been to limit the number of times that they can try to launch within an extended launch window. But if something goes wrong with the fuel-handling equipment, or thermal management inside the tanks, things can get bad.