Yes, using the power button to lock/unlock is very convenient in two situations:

When holding the phone vertical after making a phone call. The power button lands beneath the thumb of a right-hand user.

When holding the device with the left hand (forefinger will be on/near the power button) and a stylus on the right hand - to unlock, just click power with left hand and swipe the on-screen lock with the stylus.

When holding the device horizontally with two hands (e.g. after typing), the regular screen-lock slider works best.

Some thought has been put to this stuff. Two ways to accomplish the locking, really useful.