Greater chance of the stick on weights falling off than the correct wheel weight put on the outside of the wheel lip. It's really difficult to achieve the same level of balancing when you're using sticky weights, especially to maintain that balance with older wheels that were not properly cleaned before applying the sticky weights.
Personally, I used outside weights on my new wheels/tires...but if it called for say 4 ounces, I used 2 2oz weights to keep it looking decent. I've seen guys that are horrible at balancing really make it look ugly.
If you have 2 of the same weight right next to eachother, then that's cool...but if you have like a 3oz and a 1oz butted up next to eachother, that looks tacky...especially if they then counter-balanced and put like a .5oz 45 degrees off from the others, that looks really bad then...and is not properly balanced.
02 Ext Cab | 4x4 | 3.0 | M50D-R1 | 3" PA BL | 33x12.50x15 Dynapro M/T's | 15x8 Soft 8's