No, you need wear prescription eyeglasses to help you see clear. If you not wear the eyeglasses when you need, you may strain your eyes to focus somethings that do nothing but make your nearsightedness more worse. So, just wear it when you need it to see clear. In fact, i am also nearsighted and often do that. Though we not like eyeglasses, but for a clear vision and eye health, we can to wear it when we need vision aids.
That depends on your own condition. If you are slightly nearsighted, it is ok to wear myopia glasses only when needed, which won't cause any damage to your vision. If you have strong prescription, you need to wear myopia glasses all the time. Otherwise you can't see things clearly and often get blurry vision or headaches. If you suffer these symptoms for a long time, it will affect your vision and make your vision even worse.