A great resource for questions like this is cartalk.com If you enter the topic in their search box, there are multiple threads on the topic, most agreeing that it's typically bullshit.
Unfortunately, it seems were are at the point where the business model of most dealerships is to get you in the door for warranty work, then attempt to sell you any service they possibly can. In my case, I just took a 2013 CRV in for two warranty issues, both of which they failed to resolve. They did however find the time to hunt me down in the waiting area to attempt to "upsell" me with $270 worth of needless work, including replacing the engine and cabin air filters. At a cost of $40 PLUS labor. The parts cost me less than $15, and a blind monkey could install both of them in fifteen minutes, IF they needed to be changed, which in nine months of limited use, is ridiculous. The other charges were for "cleaning" the brakes and doing a 10K service, which is pretty much involves doing very little but visually inspecting a few items. Had I said yes, they would of easily made $200 for doing very little that was of actual value to me. IMHO, any time a service writer says, "we recommend that you do this", or "it would be a good idea to let us" your best bet is to say no.