In my Harlequin list I have two units of Pathfinder Rangers. Being my only two troop choices, keeping at least one of the units alive is key for me to get a victory in any objective based missions. Camping one unit out on an objective with Eldrad is an obvious start, but also makes them a bit of a priority for your opponent. Lately I have been doing the opposite and not deploying them on the objective, with some great success.
I have found that deploying the Pathfinders away and behind the objectives seems to make them less threatening. Your opponent will probably ignore them for a few turns as they are not scoring yet. Also as your opponent comes closer to you they will have to make a choice of either stopping on the objective or coming off it to get to your troops. Of course either way I plan on giving them some laughing death with my Harlequins whatever they choose.
Now here comes the ace card...
On turn four or five I will start to make moves for objectives. Having been sat at the back of the board in terrain your opponent feels fairly safe. After all it's a rough terrain test and a run move right? OK, normal Rangers get a 3D6 test, but upgrading to Pathfinders means they Ignore terrain all together making them incredibly fast moving! Within one or maybe two turns I can get to an objective deceivingly quick.
When combined with some supporting units the power of the Pathfinder is not to be overlooked.