Tension is the antithesis of a good sound. It brings with it impurities and blemishes, causes problems with intonation, makes you sound like your squeezing your tone out like the last bit of toothpaste from a tube and impedes moving freely between registers.
Here’s an exercise I use with younger players to challenge and extend them with their scales. It’s more interesting and beneficial than just going up and down a scale. Of course it can be altered as required; various keys, ranges and articulation.
This is a fabulous tone exercise requiring great embouchure control, from my friend and mentor Elizabeth Koch. Start very softly, make a huge crescendo, slur up the octave seamlessly, glide across the semitone and diminuendo beautifully!