My understanding is that winny can dry-out connective tissues like tendons and ligaments. I definately associated some tendon/ligament soreness and stiffness during my winny cycle (as well as hair shedding and insomnia...).
Some people associate deca with canceling-out that effect, but deca creates a water gap in the joint itself -- not in the connective tissue. Therfore, while the two compounds work "near" each other in the joint, they don't truly work on the same specific tissues.
Having said that, some of the other deca sides (i.e. bloat, progesterone) are still offset by winny hence deca/winny is a classic combination.