Yes. A service charge is usually 15-20%, depending on the size of the order - the larger amount is for smaller orders. This is required for large orders, which is separate from a tip which isn't required, but appreciated. A service charge is only charged for large orders, and includes preparation and sometimes delivery of a large order. One thing that I never understood prior to being a restaurant owner was why restaurants would charge a service charge for a large order, my view was, "weren't they making enough money from my order?" That was shortsighted, and now I understand, and my goal here, is to help you understand as well.
Ultimately, when a large order is prepared, it is put above all other orders. Often, we need to tell people that their orders of 1, 2, 3 pizzas, etc. will take over an hour because we are working on a large order, thus, sometimes losing more orders than what the 1 order brings in because we are dedicating our time all to that 1 order. The same goes if we are closing down for a few hours for a party or private event, we are losing revenue in order to focus on one group. If instead, we are doing this on a day we are closed, or during a time we are closed, we are basically doing all of the prep for one order, delivering for that order, and doing things we don't offer most customers; thus, doing extra for one customer. Please note, in most cases, we are driving 20-30 minutes away, then driving through a camp or wedding venue to find the private party, and hand delivering. This is well over 1 hour of additional time spend being making food. On average, there is at least 1.5-2 hours of additional time spent for large orders taking into account delivery, etc. We are also charged 3.5% to process those large credit card transactions.
So, that's the reason for service charges. It's labor intensive, the food is usually required at a specific time, and our staff and kitchen are all working to get that one order done for you. As mentioned, this is separate from a tip, which is not required, but appreciated.