God gave them wings with which to fly! We discourage clipping but there may be situations that limit full flight.
The subject is emotive but clipping a bird's wings equates to clipping their arms, in other words, it dis-(h)arms and results in negative effects on the physical and psychological welfare of the bird. The decision to wing clip should not be taken lightly and certainly not as a matter of convenience for the human carer.
If clipping is done in fear of the bird escaping from the home, look first to see how you can modify your home so that the bird can enjoy its God-given wings. During summer months when windows and doors are often left open, a wire screen can be placed over the openings to guard against escape. Common sense and a certain amount of effort can help lower the risk of your bird ever escaping.
Small children in a household are a problem. There may be one or two very conscientious family members who are very diligent when their parrot is flying around the home but if it is a household that is a thoroughfare for less conscientious family members and friends or even absent minded children, it may be impossible to ensure the bird's security and so he or she could escape, but measures can be taken to lower the risks.
If you have several parrots in your household one of them may be a bit of a bully and therefore be a problem for the rest of the group. Clipping the offending bird's wings slightly is a reasonable solution to the bullying which might otherwise impact on the physical and psychological welfare of the other birds. However, bullying should not be confused with natural behaviours in the flock to establish the order of dominance.
Sexually mature, hormonal birds may change from being Mr Nice to Mr Bad-Guy. This can be profound with the blue-fronted amazon and certain species of cockatoos. The character of Mr Bad-Guy may launch a full attack on the partner of its chosen person, sometimes flying on the person's back with the intent to do serious harm. Of course, this is a manifestation of natural parrot behaviour expressing possession and territoriality during the breeding cycle, as seen in the wild.
When this type of behaviour occurs in the home, life can be difficult for the human flock. It is better that the parrot should be clipped for these periods than risk maltreatment, human retaliation and potential rehoming but a still better solution is nurturing guidance and positive reinforcement (i.e. reward good behaviour rather than punish 'bad') before these behaviours become established.
Some owners will sentence their parrot to a lifetime behind bars because it chewed their lampshade or nice piece of furniture but chewing is natural parrot behaviour, both in the wild and in captivity! It is the keepers responsibility to provide safe items for the bird to chew - for example, quality wooden toys, plain cardboard, clean natural branches and twigs. Ironically, these owners consider wing clipping to be cruel. We would much rather these birds had a slight wing clip than spend a lifetime behind bars.