There a few reasons for Latex paint. It's water based so it's easier to apply. It can be brushed on, rolled on or sprayed on. It will dry quickly, & is waterproof once it's dry. Plus, if you don't wait to long, It's easy to clean up the mess with soapy water.
You already know about oil based paint. Over all, oil based paint is a little bit better protection for the wood but, It never truly dries. In hot weather, it may get soft & dust in the air may stick to it, making it look dull or dirty.
There are problems between the two types of paint. First, they don't mix, & you can't paint one over the other. So, I have to ask you, did you remove all the oil base paint first? If not, the latex won't dry correctly & if it does dry, it will start peeling pretty quickly. You may have to try finding a primer that will work with both types of paint.