Production layers produce eggs very well. They have a great feed to egg conversion rate. But, when they are no longer laying, there's not a lot of meat on their bones. They will make a nice soup stock. But not a bird you'd want to serve to company!
Meat birds grow out and provide a good meaty carcass in a reasonable time. CX will grow out in 6 - 8 weeks. That's what you buy in the cello packs at the grocer. Their feed to meat conversion rate is fantastic. The CX grows so fast that feed intake needs to be monitored to keep them from having joint or heart failure.
There are other "meat birds" which are not prone to the systemic body failure of the CX. Their conversion rate is not quite as good, but they grow out in 12 - 13 weeks. It's most convenient if they can be processed around this time before the major testosterone kicks in. (Testosterone = Jerk teen age punks who want to fight any male, and will gang breed any female that they can catch. Cockerel drama is not a pretty sight.) Examples of these birds: Pioneer aka Dixie Rainbow, Freedom Ranger. Each hatchery has their own named birds which fall into this category. They are hybrids, but IME with the Pioneer, they breed true enough that you could get a few generations of good meat before the genetics lead to decreased size. They free range well, and actually make decent layers.
Dual purpose birds are good layers, but do not produce as well as the production layers. They also provide a decent carcass for the table, though it pales in comparison to the CX. Their feed to egg or feed to meat conversion rates are not as good as that of the production layer or the CX or Pioneer. Many people keep a flock of DP birds, and simply raise replacement birds every year. They eat the excess cockerels, and keep or sell the pullets. When a hen is done laying, she goes in the soup pot.
For the newbie starting out, the reason I suggest doing a few layers and a few CX is this: You get good layers, you get good meat. You only have to brood chicks once that season. And you avoid the rooster drama that comes with a grow out pen of cockerels. Or just start with layers, and add meaties the next year. Keeping a rooster and keeping him well involves an extra learning curve. That may also be a project you want to delay until you've decided how committed you are to keeping a flock long term.