From: The House of the Mouse
I'm a big believer in keeping zocs on the German, myself. But odds are good that whatever is being used in picket duty won't be coming back, so the trick is to use disposable units in this duty. This includes stuff like NKVD regiments, AT brigades, para brigades, low morale rifle divisions that are survivors of turn 1 from NW and W Fronts, etc. You do have some trash units.
A picket line can slow down the landsers and separate them from the panzers...or conversely, irritate the German to the point where he starts diverting mobile units away from his main thrust to clear out the trash. It complicates life for the German. It's also mostly a 1941 thing, although tank brigades can also do this job in 1942+ (you get way more of these things than you need or can support.)
This is my take on defending as the Soviets as well. Your goal is to try to always put some bodies on the German mobile units. You'll destroy more tanks by attrition than you will in straight-up combat. If you can keep ZOC's around the panzer's you can also increase his supply path MP's needed to get to his panzers, which will lower supply deliveries and hence his available movement. Keep him tired and mired...be as much of a PITA as you can.