If you are experiencing vibration or shaking from your steering wheel or excessive Tyre wear or tyres dont seem to be lasting very long after purchase, then it is likely that your alloy wheel is suffering from some form of damage. You may have fallen victim to the 'pot hole plague' and had that awful feeling where you cannot avoid going through a pothole due to the traffic conditions and then experience that crunching sound when your wheel gets bent in some way. No matter how minor the damage is, it still will have consequences for the general ongoing health of your car. Damaged wheels also lead to MOT test failures and in the worst case the car will be unsafe to drive if a wheel becomes structurally unsafe. 
Alternatively you may have a kerbed wheel as a consequence of either clipping the kerb while moving at some speed or a gentle scrape when parking or pulling up against a kerb. Out of shape wheels will not only destroy your tyres but the vibrations can cause serious damage to both the steering and suspension components of your vehicle. 
In their worst form they will not hold air or lose hair rapidly. All of these situations imply that your wheel needs straightening and if particularly bad, a full alloy wheel repair and refurbishment will be required.