This question seems to come up repeatedly on Eyescene. I hesitate to reply as it would be oppressively repetitive. I therefore hope this page becomes a popular link instead.
I am Electra's real-life optometrist, and for obvious reasons will not be using my real name here or divulging my location, except to say that it is in the United States. I run my own business out of a small converted house, and have no affiliation with any chain or manufacturer. I have over 20 years experience.
Firstly, my professional opinion on the practice of induced myopia. Patients presenting with very slight (-1.00 or below) of myopia often refract as hyperopic using cycloplegic drops. This is a condition known as pseudo-myopia and is a result of the eye over-compensating for close work. It's very common among students, for example. Over time, if no corrective lenses are prescribed, these patients remain stable for many years. However, if no cycloplegic refraction is done, it is quite common for opticians and rushed optometrists to prescribe a minus lens. Often the young eye is able to accomodate the lens prescribed, and the pseudo-myopia can, in some cases, become genuine. These cases are easily identified by very slow progress of myopia at an age when it is normally rapid. The "myopia" never increases beyond about -1.50, and in some cases "cures itself" in middle-age.
With this exception I have personally never come across any case of an individual making himself more myopic accidentally or deliberately using a stronger than necessary minus lens. Logically, if it were possible to do this, then it follows that mild hyperopia could be cured by using a minus lens. This is not so, and the individual so doing would suffer discomfort in the attempt.
Similarly, the oft-discussed method of "curing" mild myopia by using a plus lens has no basis in logic. The individual claiming this "cure" would fall under the category of the pseudo-myopic above, in other words, he was never myopic to begin with, and the plus lens is the correct prescription.
For these reasons, the amount of time you wear your glasses, once they are prescribed is largely a matter of personal choice. We optometrists are only human, very busy, and therefore do not always make ourselves clear when we offer advice. When I suggest full-time wear to a patient, it is for his own benefit, glasses are designed to correct vision to as close to 20/15 as possible, and it is assumed the patient would prefer the optimum vision.
What we do not mean is that wearing the glasses any less often than recommended will do any harm, but that you will miss out on the opportunity. And if we suggest wearing glasses for TV and driving, and you prefer to wear them full-time, please go right ahead. Your eyes will tell you what is "enough" wear.