Is dental cleaning /scaling (done by drill like thing in office) is good or bad for teeth. is it true that it weakens the teeth by removing layer. ?

No: It is done by hand scalers and ultrasonic scalers. It does not remove any significant tooth structure and therefore does not weaken the tooth. It is good for teeth because it removes deposits on the teeth that can cause bone loss and eventually tooth loss.

Should not: What you are probably referring to is an ultrasonic scaler. When used correctly it should not damage teeth. If not used properly, it can remove tooth structure. If things don't feel right during the cleaning, voice you concerns immediately.

Good: A dental cleaning is typically done with an ultrasonic scaler and hand instruments. The goal of these instruments is to remove that "bad" stuff like plaque and calculus carefully. The hygienists who is performing the cleaning will adjust the power according to amount of plaque and calculus and therefore avoiding damaging or weakening teeth in the process.

It's actually good: Not sure where you're getting your information from, but the only things that should be removed are the calculus deposits from your teeth.

Recommended: There are many good reasons for having your teeth professionally cleaned. To keep your teeth, to prevent gingivitis, to have whiter more attractive teeth and improve your general health. It's actually safe when performed according to current standards by your dentist or dental hygienist.