Now, I am going to put-forth my conclusion, after having weighed several perspectives.
True, a POA holder i.e. an agent cannot replace the principal in the witness box. Certainly not, when the aspect required to be judged or questioned relates to something that the principal himself is competent to narrate or explain. While being crossed or while deposing about events known only to his person, which cannot be efficiently conveyed through another, personal events wherein an examiner requires the actual person for questioning, etc .. hope this is clear.
Reference has been made to:
Shambhu Dutt Shastri Vs. State of Rajasthan, 1986 2 WLN 713 (Raj).
However, the above principle does not apply to situations wherein the agent acts on behalf of the principal through an allowable agency. That includes, signing of documents, authenticating within procedures, agreeing, affirming, crediting or depositing, appearing formally etc.
WHEREFORE, a POA holder can certainly appear and plead or pray on behalf of the principal. A POA holder can definitely and absolutely represent his principal in legal proceedings, likewise on his behalf, as a 'party-in-person'.
I did check this up with a few reputed 'senior counsels', that my Dad introduced me to. They also told me about situations and circumstances wherein, such representation as a 'party-in-person' has been done at the high-court, in several instances.
So, that should leave no more doubts about whether a POA holder can represent his principal, as a 'party-in-person'.
Yes, it is permissible.
Only when it requires a person to appear or depose in a witness box during court proceedings, he cannot rely on a POA, but has to appear in person.