Wreck markers are cover (+4 def) and difficult terrain (half movement except Vs pathfinder/flight) so quite nice to put on your side of the table to protect your stuff (widowmakers are def 20) and +4 def to a squishy support caster is always nice!
I have read a battle report where a player finished off his own jack so he could get extra safety for his caster from assassination as that was the only way the opponent could win the next turn.
Nb. Also to sell wreck makers to Khador players as its unusual to have the motherlands jacks wrecked