Does the IS of Canon EOS70D need to be on all the time?

The 70D fuselage itself has no IS system. Canon's IS technology is applied to the lens. Its main function is to prevent slow shutter speed, achieve anti-shake effect by correcting lens displacement, and increase the success rate of shooting. Whether this is turned on or not depends on your actual shooting scene. In some cases, it doesn't matter whether it is closed or not, even it should be closed, for example, when shooting fast-moving objects. Of course, it doesn't matter much if it's always on. In fact, you can try it by turning off IS and turning on IS in actual shooting, and compare it to gain more experience.