At less than -1, glasses might be needed for far distance, like reading the board. Watching TV is still OK, maybe with tolerable shadow. There is no need for glasses for reading, computer, etc. Driving might be OK, although roadsign might be a little bit difficult to see. Glasses should also not required for night vision.
People who need -3 correction might need it more for outdoor activity and night. Driving is illegal. Wathing TV is almost impossible unles you are sitting close. Computer and reading is still OK without glasses. Nevertheless, it might be difficult to do outdoor activity like shopping.
Those who needs -5 correction will generaly have a hard time to use computer without glasses. Watching TV is quite impossible within normal distance. Glasses is almost required for outdoor activity, like going shopping. Reading is still possible without glasses, although the book should be close enough than normal reading distance. They will certainly need glasses in unfamiliar environment. Signboard will be hard to see, if not impossible in good light.
I need -10.5. Without glasses, I can see my 14” laptop LCD, but the writing is only undistinguishable black line. Tv is only shadow of changing color. Going to the crowd without glasses is a joke. I can only see colors moving, flat face, some colors with no shape in the stall. Walking at night in an unfamiliar area is not reccomended, since any directional sign is useless. I would be lucky if I can notice a signboard, let alone reading it.
This website give you simulation of driving without glasses for various prescription: http://www.eyeland-design.com/webtools/53828496ca1045c06/53828496bd08d7c0c/index.html. One truth, though. After you pass certain prescription, it doesn’t matter what your glasses prescription is.