The signature ingredient in all of Plankton's menu items and as one of several major factors that causes the Chum Bucket to attract no customers, the taste is highly considered foul in contrast to Mr. Krabs' Krabby Patty.
Plankton continues to use chum in most of his products, despite its foulness and overall toxicity, as shown by many having vomited after eating it.
Chum is actually made from live fish, which serve as the series' characters. The fact that chum is made of fish means the whole point of Plankton's business is to make the Bikini Bottomites engage in cannibalism.
Some characters have gained the habit of eating chum despite tasting horrible to the customers who have already eaten it.
Nat Peterson comes to the Chum Bucket and orders a chumstick. He then goes back the next day and the day after that, becoming Plankton's only regular customer, and the only person who actually likes his chum. However, in the end, it is revealed that he only ordered chumsticks because Karen paid him, and he actually hates the food, so much that he already had to go to the doctor twice.
Chum can actually be used to help pull off crimes and as a result, the criminal community holds Plankton in high regards.
Chum can actually cures people back to normal after they mutated into Krabby Patty zombie monsters.