A turntable is a precision instrument with several delicate, independently moving parts: the platter, the counterweighted tonearm, and the tiny, easily snapped stylus. Left loose, these parts swing and collide during transit and can ruin the cartridge. Immobilizing each part before you pack is the whole game with a record player.
Pro tip: Photograph the counterweight and anti-skate settings so you can recalibrate exactly at the new home.
Watch out: The stylus snaps with the lightest contact. Always fit the stylus guard or remove the cartridge before packing.