To clip or not to clip - that is the question!
Clipping your cockatiel's wings is, in most situations, the best thing you can do for your pet. However, there is at least one situation where you should keep your bird flighted--if there are dogs or cats in the house that might follow their instincts where birds are concerned. That's right... your sweet cat or cute puppy might play a little too hard, injuring or even killing your cockatiel, so you need to allow your bird to fly away from this type of situation.
If, however, you have no dogs or cats, or if other pets are not allowed in the same area as your cockatiel, then you should clip your bird's wings for its own safety. There are so many household items which can cause injury to your pet if it is allowed free flight. Windows, for example... how many times have you seen or heard of outdoor birds that run into windows because they think they are clear space? Your indoor birds cannot differentiate between glass windows and open space, either. Other hazards are: mirrors, open windows or doors, running ceiling fans, open toilet bowls, pots of water on the stove, hot stove burners, and many more.
Don't let your bird be a casualty. Judge the situation objectively and clip your bird's wings if necessary.