Firstly, withdrawal from Ghajar is a quiet but significant overture to the United States, which has been slowly ramping up its relations with Lebanon since the 2nd Bush administration. The move, in fact, is seen by some as a move by Israel to try to take US pressure off of Israel in the wake of this week's intense settlement freeze negotiations. Regardless of the motivation, the US (and the UN as well) view the withdrawal positively, which strengthens the US-Israel relationship, and gives Israel some maneuvering room with the US in peace negotiations.
Secondly, the withdrawal undercuts Hizbullah, though it does not undermine it. Hizbullah was founded as a movement which violently resisted Israeli occupation. By withdrawing now, Israel demonstrates that Hizbullah has nothing to do with its withdrawal plans. It also undercuts Hizbullah just as the Special Tribunal for Lebanon is about to release an indictment which Hizbullah has threatened to violently oppose. While Hizbullah has already begun to shift its focus to "national resistance," the Ghajar withdrawal nonetheless chips away at Hizbullah's legitimacy in opposing the Israeli occupation of Lebanon. This will somewhat mitigate their ability to violently respond to the STL indictment. It won't be the straw that breaks the camel's back, but it does tighten the scews a bit on the organization.
Most importantly, the Ghajar withdrawal is a case in which Israel is actively reevaluating the status quo to improve its security. There are many areas in the security sector in which Israel would benefit from this process, and the withdrawal from Ghajar is another example of the IDF acting pragmatically to increase Israeli security. The IDF and Israeli government have wisely realized that the costs of occupying Ghajar outweigh the benefits, and have acted accordingly. Institutionalizing this kind of evaluation is one of the most important steps Israel can take to ensure its continued long-term security, regional stability, and strong relationship with the international community and the United States.