Depends on the gear. On 1st and 2nd it’s a good practice to not give any throttle- they are very torque sensitive gears and it’s a good idea to gradually speed up and transmit power.

In higher gears, the effect is lesser. It’s still not a great idea to throttle when clutch pedal is depressed partially. Releasing it completely and smoothly is the art of driving a manual.

I’m sure they do it in races for response, but those clutches are meant to last one or a few races. Our cars that we use everyday we expect the clutch to last years.

A proven way to check if a car’s clutch and gearbox are in good condition (a good mechanic would check this) is to see if the car moves smoothly without any throttle on first gear. If you’ve conditioned the car by throttling during clutch release, there is a chance of some clutch damage and it may be a bit jerky. This will represent poor driving style and can overall mean that the vehicle was abused a bit. It may affect overall perception of ownership and resale.