Yes, what Jayco said is basically true. You will find that over the years it will tend to become hard, and that's when you have to watch for cracks. Tacky is good, means it is still flexible and will be less susceptible for loosing its grip/seal.
As a precaution twice a year you should check your entire TT (roof, wall joints, windows, etc.) to insure that all seals and caulking hasn't been compromised (also keeps your warranty valid).
Don't worry about the roof caulking getting dirty, nobody looks up there anyways.