I've done this tour several times. When the park gets crowded during the holidays, it's a good time to be on a tour!
You have headsets so you can hear the guide tell you all about Disney at the Holdiays. They explain about the decorating, the themeing, even the treats. Did you know that the Gingerbread House in the Haunted Mansion is real gingerbread made by
Disneyland pastry chefs? You get to sample samples of the holiday fudge, you get to ride HM Holiday, It's a Small World Holiday, the train from New Orleans to ToonTown station. They take you through the different lands and show you the decorating and themeing. At the end of the tour you get hot cocoa in a souvenier mug, a treat (it's been a cookie, or a rice krispey treat depending on what they have that year) a collectible holiday tour pin, and reserved seating for the parade. It's nice to be able to sit and sip the cocoa and wait for the parade. The parade is always at the end of the tour, which is about 2 hrs long.
The parade seating is part of the tour, not something you come back for later.
I always enjoy this tour, especially on a busy park day.