Phase Delay OR Port extension on VNA Cal

Dear All,

Can some provide information on the occasion on selection between port extension and phase delay on the network analyser calibration ? I already knew that www.vnahelp.com has some information but it is not clear enough.

BR
Rayengine

phase delay not including line losses and connection discontinuety.it can be use in a non-stringent deembedding.
port extension is more complicated, it always use software to fit measurement result to deembedding.