When it comes to attending auditions for commercials, the jury is out regarding whether landing a commercial can advance an actor's career. As a rule of thumb, the type of commercial you're auditioning for, and your goals in attending the commercial audition should determine whether you attend.
Regarding the types of commercials you could possibly audition for in a casting room, there are basically two types: Commercials that will air on television (or the web), and commercials that are filmed on "spec" and turned into a contest to win an award (think the Doritos Superbowl commercials.)
Commercials that air on TV are by far, the most lucrative opportunities- especially those being filmed by large, nationally recognized companies. Spec commercials, on the other hand, typically don't pay, but if you're an actor looking to build your reel, then often times, the footage from spec commercials can help add variety to the body of work you feature on your demo reel.
So in a nutshell, when you're thinking about whether it'w worth making a trip to a casting facility to attend a commercial casting call, be sure to a) find out what type of commercial is casting, and b) if that commercials matches your goals of getting paid, gaining exposure, or simply getting more footage for your actor's reel.