When the cable on the ESC is loosed, so you need cut off the original shrink tubing of the ESC, solder the cable back, then protect your ESC with a new shrink tubing again.
When you need to re-program the ESC with the latest or a different firmware (eg. SimonK Firmware for MultiCopter).
This Shrink Tubing is suitable for:
ESC (Electronic Speed Controller)
It is hard to tell which diameter of the Heat Shrink Tubing is suitable for your ESC because the size of ESC is different according to brand. But for your reference, Ф28 was used for "RCX07-003 RCX 40A ESC". You need to measure the dimension of the ESC carefully by given that the width of the Ф25 Shrink Tubing is 4.1cm so you know where to start with.
Width: 4.1cm (The Width, Not Diameter)
Particular: 125°C VW-1
Shrink Ratio: 40% - 50%
1 x High Ratio Heat Shrink Tubing (Black / 25cm / Ф25 for ESC)