The dinner package guests wait in line on the left, the others on the right. The difference is that the dinner package guests know they will get a seat, and very likely a good one. (They do not oversell the seats reserved for dinner package guests.) The others get what's left (roughly half the seats), and are not assured of a seat.
Is it worth it? It depends, on the makeup of your party, your dining habits, which restaurant you go to, and what you're willing to pay for an assured seat. See
http://allearsnet.com/tp/h_cpfaq.htm for the pricing.
A party of all adults who want to order an appetizer, expensive entree, and dessert can actually save money at some restaurants.
In our family of four, I'm the only one who can eat that much and I usually don't wish to. So we would ordinarily just order entrees, and possibly dessert. Furthermore we typically have a 20% discount available which can't be used for the dinner package. So at the Tier 2 and 3 restaurants, we would pay at least $60 more for the dinner package than for an ordinary meal. This means we would pay $15+ per person for our "tickets" to Candlelight Processional. For many people it is worth this much. I'm not sure.
Instead we usually select the Garden Grill restaurant, where the package price is not that much more than what you'd ordinarily pay with tip. Since we enjoy that restaurant anyway, it's a good deal for us.
If you don't get a package, I suggest going to the 5:00 show, for which the lines usually aren't as long. The downside is that it's not completely dark at the beginning of the show, so the "candlelight" effect is not as good, but it's still a great show!