PNGs have the ability to have transparent backgrounds while JPGs don't.
Having a transparent background just means that the image isn't constrained to having straight edges and a background color. This means that you can insert images into your presentation and have it conform to your presentation's background color, which will make it “blend in” and look more professional.
You’re probably more familiar with JPG images because it is a widely used image file format. Most cameras and cell phones take pictures in the JPG file format because it is able to compress the image’s file size and still look pretty clean.
The downside to JPG files is that you can’t have a JPG image with a transparent background.
Here is an example of a PNG next to a JOB. As you can see, the PNG allows you to see the background of whatever it is on top of: