The Rebbe: Davening in a Siddur 

It's difficult to do ..i understand tho....

not that they specifically the People watch the Rebbe, but that they are not concentrating on the Creator, blessed be He.As we know while praying we need to place Hashem before us.

And yes, towrds the end The Rebbe was explaining not to look at him during prayer.

Comes in handy,when to or for of them Tzadik come Together for completing a certain period of time, needed it .