Alas, SDSTADD TubaDiva isn’t entirely correct with this answer. It’s true that racing slicks have rough spots, though it always seems to me that they have more after a race than before (picking up rubber from the track, throwing chunks in corners, etc.).
Heat is the main reason for drivers to weave. Heat not only increases grip, but it keeps the tire’s air pressure up. The grip difference between hot and cold tires is immense, and low driving speeds allow the tire to cool. If you watch Formula 1, you’ll see drivers weaving during yellow flags. If the purpose were to get rid of rough spots, weaving during the middle of the race would make no sense. However, if the tires get cold during the flagged laps, the cars would have a tough time getting to speed again.
I just thought you’d want the opinion of a driver (not F1, though).