Like most professionals who've ever had to give a presentation, I began using Powerpoint 10+ years ago as a presentation tool. Over the years, I've created more and more elegant documents, slideshows, etc., and have recently begun using Powerpoint to create digital and print ads, social media posts, posters, brochures and other collateral materials. I've appreciated how easy it is to place text and images, adjust colors, create transparent images, rotate and layer elements, create animations, and much more. Powerpoint is really a fairly intuitive tool for the professional who is capable, but not a graphic designer by trade. There are many things that Photoshop does better, of course, but I'm amazed at how much I can do with Powerpoint with far less swearing. So far the biggest limitations are the size of document you can create (under 50 inches); it doesn't set up in pixels, and it takes a little finesse to produce a high-res output. For my small marketing consultancy, where it helps to keep as much work as possible in-house without paying outside designers for certain types of projects, Powerpoint has become my constant companion. I produce proposals, plans, mockups, and even some finished work all from this one, indispensible program.
Admittedly, this is not marketed as a graphic design program, but there are only a few small things that would make Powerpoint an easy-to-use tool for simple design: 1., a slightly-easier-to-use "remove background" tool (that doesn't leave the resulting image pixelated); 2., the ability to export or save documents as a Photoshop PDF; the ability to set up a document in pixels, 3., the ability to select dpi.