What exactly do the Chinese get out of occupying Tibet?
Tibet contains very rich mineral resources.
Tibet has the world's largest deposits of uranium and borax, half the world's supply of lithium, the second largest copper deposits in Asia, and the largest supplies of iron and chromite in China.
It also has more than 40% of China's present supply of bauxite, gold, and silver, and extensive reserves of oil, coal, tin and zinc. In addition, Tibet has huge tracts of timber.
Since China's 1949 occupation, it has aggressively exploited these resources. Forests have been clear-cut to provide lumber to China's eastern cities. The pace of mining, usually open-pit mining, has accelerated in recent years. Indeed, two of the five pillars of the Tibetan economy, according to Chinese planners, are mining and lumbering
From: http://www.tibetjustice.org/reports/apec_paper.html
It is also a precedent they like to use as justification for claims they still make, but but press politically more than physically, on Nepal, Bhutan and other central Asian territory. To lose it now undermines their "One China" policy which they use to give credibility to their claims on Hong Kong, Taiwan, Inner Mongolia and Xianzhang (the western province inhabited by the Uiguirs who are Muslim).