From the BFBB Wikia:
Hansis the character that drags you off screen when SpongeBob walks for too long on sand or hits a certain trigger that will place SpongeBob at a previous checkpoint. When the hand is disabled, it does not prevent SpongeBob from getting grabbed by walking on the sand, it will only prevent SpongeBob from getting grabbed by triggers. When you enter a loading zone while the hand is on the screen, it will disable the hand, preventing him from showing up until he is re-enabled by being in contact with sand for to long.
This glitch, found in 2011? by ???, is perhaps the most valuable trick in the game, especially useful for speedrunning. It allows the player to access many OOB areas, and it is used in conjunction with other tricks in the game.
Hans can be re-enabled by standing on a death plane until the hand takes you away again. This allows you to take advantage of OOB death warps in certain parts of the game.