It appears it is a done thing and I have only done it on when finding out I'd ran out of swabs.
That being said, I've come across someone who used a lint cloth by wiping it across the sensor with his finger, which is crazy.
I've only just discovered the A1 offers the option to close the shutter when the camera is powered off (in the setup menu) which should help along with loupe illustrated by Footman with anything that is missed.