renault sport spend loads of money on car handling just for you to put on dangerous spacers duh !!!
hub centric spacers are not dangerous! that's a stupid thing to say! exactly the same fixings as your standard wheel to the hub, and being hubcentric they locate on the hub and also the wheel to the spacer...
what they do do is alter all the damper/hub/steering axis geometry at the front, Renault went to massive lengths to ensure the front wheels rotate around the imaginary line that is created by the very complex hub on the front of the car (this is also effected by lowering and stiffening the car to some degree as the lower horizontal drop link will effectively be in the wrong axis but its very minor and offset by the extra stiffness so effectively you don't notice) by adding a 20mm spacer you are throwing the relation between virtual steering axis and the centre of the actual wheel, this will effect bump steer, torque steer, turn in and also tramlining all to various degrees... plus it loads up all your wheel bearing by a good chunk more... but yes on a lowered car it looks a bit better, the honest answer is try it
as doogle says the cup cars ran hub spacers as the rear of the car is not effected and these don't load up wheel bearings as they space the entire hub outwards effectively
the cup cars also ran 5mm front spacers as the small increase in width benefits outweighed the negative smaller effect on the properties mentioned above
I will also add that if someone made an adapted bottom arm that was slightly longer with the lower horizontal drop link mount point moved outward by the same amount to me that would negate all these faults mentioned, increase camber and have only positive benefits that I can see, it would only be a tiny amount, one day I will do the maths and work it out correctly this mythical distance and maybe take the plunge and cut my bottom arms up
it also wont effect the virtual steering axis by more than a few mm, best go see my friends with tig welders!