Why is the minhag in yeshivos for the shliach tzibbur to wear a tallis by maariv— from the poskim (Mishna Berura and others) it is clear not to (except on Yom Kippur and maybe Friday night)? What is peshat in the minhag? Is there a source supporting this minhag?
The reason for it is because of kavod hatzibur, (respect of the congregation). Because the chazon is representing everyone, it is in their honor that he wear a tallis.
Pri Megadim Eshel Avrohom 18-2, also see Magen Avrohom there.