Because you only have a partial keg, the CO2 has to fill the head-space and carbonate the beer. You'll have under-carbonated beer. I would pressurize the keg.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk