If your slick tyres are new then i would suggest you spin them up on the wheels and see if any weights actually needed , the lead weights are a pain in the arse , they dont stay on unless well taped , you dont want lead weights spining off on a race track ,they also get in the way of caliper clearance etc...
A slick tyre will also move around your rim over the course of its life , mark 1 and see , this renders balancing useless.
If your tyres are used and covered in "pick up " then dont bother balancing them , the rubber will move around so much after theyre warm that its a waste of time .
You must be sure your rims are straight tho , spin then on a balancer without tyres to check this .