The waterfall methodology has gotten a lot of flak over the years ever since agile became mainstream. However, I want to clear the air and say that waterfall is not bad in some situations! You should not automatically assume that if you go to agile that everything is going to get better, because in some cases you could get worse.
For example, let's say someone comes to you and gives you a full design doc and asks you to implement it as is. Sure, this is rarer than a unicorn in Texas, but it could happen. If you choose to use agile, you're going to waste a lot of your time in meetings and planning that just isn't necessary. You're also going to waste a lot of money by having a full staff working during those meetings.
So let's see how waterfall is more useful in this situation. First, you can create the entire schedule up front with only a few key people. These people are going to be the best of the best, so they are expensive. But, you're going to get very good quality of work that is indeed going to save you time during the course of the project. And after this initial planning phase, you don't need to keep them on the project anymore. They've just done the work that 90% of engineers are not capable of doing, accurately planning development.
Once the work starts you can hire the exact number of engineers required and set them off on a path accurately mapped out for them. They'll be able to hammer through all the tasks and will do it without a single meeting. What are you going to meet about? All the questions should be answered in the documentation from your experts at the beginning.
Project completes on time, customer is happy, and you get paid. Done.
Ok, ok, ok. I know that is a perfect world but hopefully you get my point. In SOME cases waterfall is the correct methodology to use!