What effect does regrinding have on the milling cutter?

End

If the end geometry is too heavily worn, this will be cut off and reground. As a result, the tool length (cutting length) will be reduced by the dimension "x" that has been cut off.

Rake faces

Regrinding on the rake face reduces the cutting diameter.

Includes

Regrinding on the periphery reduces the cutting diameter.

Neck

If the neck of a tool is reground, this only affects the diameter.
The length of the neck remains unchanged.