Why not? What are the negative consequenses? I'm not trying to be confontational I just never thought about it.

More wear on the cylinder walls form cold metal/oil, and incomplete combustion letting raw fuel into the oil.

Starter health is important to your diesel.
http://www.peachparts.com/shopforum/diesel-discussion/107318-starter-health-important-your-diesel-post739798.html

Battery selection / Charging System / jump starting / cold weather battery issues
http://www.peachparts.com/shopforum/diesel-discussion/141516-battery-selection-charging-system-jump-starting-cold-weather-battery-issues-post1058189.html

Battery for your Diesel
Battery for your Diesel

Asked and answered.

If you've got a block heater and can alleviate some of the burden on the starter and the very poor oil flow from conventional oil, why not take advantage of it................!

Omegaman uses punctuation

My old engine with the bad rod had a nice condition block heater in it, couldnt get the thread reducer out with it, no biggie there, thats easily replaced, the biggie came when I was unable to remove any of the plugs in the replacement engine so that I could put it on, froze in good enough to bust off a tool in them with a cheater pipe....I probably coulda drilled them out, but it was too much trouble to get into, so the heater still sits on the shelf in my shop...

1980 240D w617 motor