Wolf Scouts tend to make your opponent second-guess his tactical choices; after all, would you like a meltagun, a combi-melta, and a 5 man squad equipped with meltabombs turning up behind your Leman Russ equivalent? No, and neither would anyone else. Two squads are even worse, and considering both squads cost about the same as a common layout of a Grey Hunter squad + transport PUT TOGETHER, you can see the point of the psychological distraction.
Simply put, this forces the enemy forward, and for an army focussed around midfield combat, this is good; this allows you to claim objectives, double-tap boltguns in their face, or charge if you need to, depending on the situation. If against an even more aggressive army like Blood Angels, use it to take out any backfield fire support by tying them up in CC, or if they have none, try and break up their advance by charging a unit advancing down the flank, or reinforcing your units at your table edge. If playing a defensive army however, your Wolf Scouts just came into their own; pop a fire support tank or tie up some heavy weapons etc.
If your opponent spreads out along the table edges to stop you coming in with BEL, good news! You just affected their deployment, the phase of the game that wins and loses battles. If they try and stop you coming in to affect them, that generally means half a board edge away from their main castle. For everything except Guard, they aren't numerous enough to do this without seriously hampering either their list or their castles frontal defence; either way, you have an advantage. For Guard, the only type of list that is likely to be able to do this is foot Guard, and if you see this in a tourney, expect an easy win -but not a given as foot Guard can and does win when people drop their guard. (Check the pun!) To give an example against Guard, the manager of my FLGS moved his Leman Russ Plasma Spam Tank (TM) too close to the edge and then proceeded to be immobilized shaken/stunned for the rest of the game, eventually granting me a close draw. I hate to say it, for it is a cliche, but one armour save swung the game. If you want a battle report post, put it in comments
All in all, the following unit is probably a good minimum for Wolf Scouts:
All for about the price of a las/plas razorback
Throw in a Wolf Guard with combi-melta and/or meltabombs on the squad for gravy, if you have more points.
All in all, Scouts do more than their points cost suggest, and they repay you in the time-honoured currency of "messing with people's minds", which is a extremely fun currency to use! For the points, the above squad is well worth it, and sometimes earn their points back in ways you don't expect.