Training for a marathon or even to get into shape is a good thing. However, people will find that they need to keep track of a lot of information when they are training to guarantee they are going to get the right amount and the right kind of training. The problem is it can be difficult to track this information - which is where pace calculators come in. These can help you learn more about how your training is going, but also how to ramp up training successfully for the time you put in.
The first reason that you should be using a pace calculator is this will help you know how many steps you have taken. This is going to help you determine how fast you are running, but also let you know if you are getting the right amount of steps to complete their training goal. Without this, you're simply guessing at how you're progressing.
A second reason to use a pace calculator is to help you better understand the pace you need to set to get healthier. For example, some people may want to run a specific time frame while they are training and do a certain distance. You can't hit those goals if you don't track them.
And devices are available now that go well beyond basic pace counting. You can get devices and apps for your smartphone. You can get software to download the data, and manage and track all of your training and runs. You can go too far with this stuff, unless you're a professional athlete of course, but it can also be fun to see your progression over time.
Oh, and make sure you choose the right running shoes to start with.