Features of a good electrode (wrt Pt) -
1) good electrical conductor so it is usually a metal.
2) Some reactions require an inert electrode that does not participate and platinum is a inert metal
3) Platinum is added to the cell diagram/redox reaction when there is no solid already in the anode or in the cathode of the cell.
4) Pt provides a large surface area and thus acts a catalyst by adsorbing H2 gas (SHE/NHE-Concentration cells)