What's the thinking behind this please?
A write sets the timing for the pulse, but if there's no pin attached to the Servo object, it effectively changes the default position for the Servo.
Say, for example, your application always parks the servo at zero degrees.
At startup, the default behaviour of the Servo object would be to move the servo to 90°, and you would do an immediate write to set it to zero. It may well twitch.
Do the write before the attach, no twitch.
Or, you could just put the horns on with a ninety degree displacement.