Daf Yomi - Yoma 51 - Open, Shut them .....

A student of the Rosh brings from his Rebbe that they used to fold over the end of the peroches on Erev Yom Kippur to enable the kohen gadol to enter into the Kodesh Kodoshim on Yom Kippur. The rest of the year it remained closed, so the kohanim should not see that area (between the other curtain), for that might have the sanctity of the Kodesh Kodoshim.

Rebbe Meir holds that this is the reason why the kohen gadol would walk between the shulchan and the mizbeach and not by the wall, for then he might feast his eyes on the Kodesh Kodoshim (Rashi).

Reb Dovid Meyers in his Sefer Mileches Hamishkan brings a proof to this from a Mishna in Menochos which states that there were kohanim on both sides of the shulchan placing the lechem hapanim and the bezichin onto the shulchan. If the peroches was opened all year, why weren't we concerned that they might gaze at the Kodesh Kodoshim? Obviously, it was closed during the year.