If you are not presently lifting the front end of the skidded log, then a cone will likely help a lot.
I at least lift the end of the log and just drag the tail because I don't want all the dirt in the bark (plus the rut in the woods and road). The cone works well too when pulling the log through the woods as it lessens the tendancy to hang up on roots and other trees. But it just guides the leading end of the log. The log can still sideswipe other trees and cause the bark to be damaged which is not good for the remaining stand. Some trees stay along the skid trail for just that purpose however.
Personnaly, I wouldn't spend the $$ on a cone, but then I don't have the steep woods that I can't usually get close to the log with my tractor. If I was winching logs up a slope, then I'd have a cone for sure. Wouldn't like hauling it around however, and trying to keep track of it so it was available when needed.