...When they can't figure out how you do it and you don't get caught.
Traction control has been banned from Formula 1 for years now but anyone sitting by the hairpin turn in Montreal was well aware of Red Bull's superior traction out of corners. Vettel certainly smoked everyone off the line at the start and had gained a 2.5 second advantage on Lewis Hamilton by the end of the first lap. There is no doubt the RB9 is hooked up.
A sharp eyed reader of Autosprint noticed
Vettel's Webber's car was leaving the curious set of tire marks you see in the picture: It looks like traction control, it smells like traction control, it certainly sounded like traction control.
What's going on here? As you can well imagine, if a viewer can spot this on TV, rival teams have been all over it for a while, complaining to FIA repeatedly we're told. Despite the best efforts of FIA technical personel, nobody has been able to come up with anything illegal on the RB9.
Traction control as a specific component is banned but its function is now duplicated by all, with different degrees of success, via engine maps that manipulate torque curves and use partial firing of cylinders to achieve the a similar result. Mapping is one of the black arts of modern racing and one essentially impossible to police.
Even with the insane tech of today's F1 the old maxims still apply: " if you 'ain't cheating, you ain't trying" and " it's only cheating if you get caught".