The benefits of Balfour were mental in the sense it gave hope to the zionists that their vision of a Jewish homeland could become a reality As an actual document it became irrelevant because facts changed on the ground. Balfour talked about creating a Jewish HOMELAND not a Jewish STATE. It was theoretically going to be a binational state with Jews & arabs living side by side, in reality an arab state with a small Jewish minority. The zionists for the most part were happy with the homeland rather than state idea and it wasn't until late 20's - mid 30s when hostilities between the Jews & arabs of mandate Palestine increased that the more hardline zionists decided nothing short of a Jewish state could be considered acceptable and this idea eventually spread became mainstream zionist ideology. Then there was WW2 which created a Jewish refugee problem and the west started to become sympathetic to the idea of a Jewish state. The League of Nations which had given the British their mandate to govern Palestine and lay the groundwork to create a Jewish homeland was dissolved and replaced with the new UN and in 1947 the UN voted to create a Jewish state which was the final nail in Balfour's coffin then in 1948 Israel came into existence and when that happened everything that Balfour was pretty much flushed down the toilet as a document of any relevance.
UN agency warns school may be delayed for Palestinian refugees due to lack of funding (AP)
from the article: Is the Balfour Declaration still relevant?