My first digital in 2003 was a 3 mp and gave excellent 6x4 prints and pretty good A4 size. With a higher mp you will be able to crop photos down to a smaller area and it will also give a sharper picture on your TV if you display that way. A 12mp should enlarge to poster size with little trouble. Provided the camera is set to the highest resolution that is. 12 mp cameras are so cheap now that I wouldn't hesitate. I think the cropping results would be where you would benefit most in normal day to day use.
OnePlus 5T review: Hands-on