Well there are several right answers about the topic of “Do we buzz when we play?”
I know some good players who can NOT free buzz. I know some good players who can NOT free buzz very well. I know some good players who can buzz.
First there is a vibration setup in the air in the tubing of the trumpet. And that vibration is responsible for the sound that we hear. Now how does that vibration start? If we wrap our lips around the lead pipe and blow all we get is a hiss. We can hear the air move but there is no vibration or tone. So then the lips have a part to play in this.
Players who can NOT free buzz need to get feedback in order to produce a trumpet sound. This feedback is from the return of the waveform that they blew into the mouthpiece. They blew air through the lips it met some resistance and some of it returned to the lips adding a slight amount of back pressure to all of the lip surface. This helped them to complete their buzz and a note was produced.
The resistance that sent the wave back is actually from multiple sources:
1. The bottom of the mouthpiece cup
2. The mouthpiece throat
3. The mouthpiece back bore
4. The ambient air pressure in the horn
5. The taper in the lead pipe
6. The soft boundary at the end of the bell
What does the feedback actually do?
Well it closes the lip aperture enough to force a buzz to happen.
How does that affect trumpets or cornet?
From low g to g on top of the staff it has little affect. As you ascend from g on the staff up it requires more and more feedback to make the buzz. There is a point where the mouthpiece and the horn can NOT add enough feedback for the range to go up any more. The waves no longer return as the soft boundary is now past the end of the bell. The player resorts to feedback in the form of arm strength and mouthpiece to lip pressure to close the aperture. Now the problem begins. Endurance, tone, range and everything else is hampered. Depending on your setup and playing requirements this problem can range from minor to very serious.
Why free buzz the lips?
If the lips already have a small enough aperture that you can buzz then NO feedback is needed. That includes arm strength and mouthpiece to lip pressure. I want to state for the record that there are people who can free buzz a high c and many can even free buzz a super c. However the ability to free buzz a middle c means that there is less need for pressure. The higher ones are just gravy as it were. There is always a point where the lips need some feedback. But if that happens over super c then that player has one heck of a lot of endurance. Although it is hard to break old habits and learn to free buzz; that ability makes playing the trumpet easier.
Is it for everybody?
Well if you are happy with your endurance then it may not be worth the effort for you to learn this. If you have playing concerns then it is worth the effort.