Did you know there is a standard for carpet fitting?
This standard is BS 5325
(The Installation of Textile Floorcoverings)
It states amongst other points that any carpet over 5 metres in width or length must be power stretched.
This does not mean give it a good hard whack with the knee kicker as this tool was never designed to stretch carpets, only to position them!
If the knee kicker is used to stretch the material it is more likely to damage the product (and the installer) than apply the correct tension.
If the carpet is stretched with the correct tools and the correct stretching pattern, there is no need for what is commonly known as a re-stretch.