Research routinely supports that social media posts with images get greater engagement from followers than posts without images. Some times 140 characters is not enough time to get your message across so a cool high end graphic would be helpful.
The days of Photoshop being the only graphic design app are gone. Most people do not need the power of a full blown desktop graphic design program. A web service like Canva is great for people in front of a computer. Canva easily produces very cool, high quality images, but if you are out and about you are out of luck.
For people on the go, there are a few mobile image apps out there that create cool social media style graphics (like WordSwag) but they can require a little bit of work to make your image look great.