As already said, it is recommended that you tell your co-workers you're leaving. They'll find out on the first day you don't show up to work anyway. While you may not care what they think and may not expect that to be a problem, you never know. I've had employers ask me about co-workers from previous jobs who had applied at my new(er) employer. So being the "person who just left, without saying good-bye" could come back to haunt you.

Also already noted, someone else will have to take over your work. Unless what you do is very simple, it may be necessary for you to update a co-work on what you're working on, so they can take over more smoothly. While we don't know exactly what your boss said, he may be expecting you to initiate this; failure to do so could affect future references.

As for people thinking negatively about you: I've worked in places where the opposite has been true when I announced my departure. Sometimes I've found that people thought more highly of me than I realized. Other times I heard things like "You got a job at {insert perceived great workplace here}? So cool! I'd love to work there. If they have another opening, please let me know."

Also, there's the human factor - people will want to say their good-byes; if you just up and leave, they are more likely to think negatively about you than if you give them some advance warning.

As already said, it is recommended that you tell your co-workers you're leaving. They'll find out on the first day you don't show up to work anyway. While you may not care what they think and may not expect that to be a problem, you never know. I've had employers ask me about co-workers from previous jobs who had applied at my new(er) employer. So being the "person who just left, without saying good-bye" could come back to haunt you.

Also already noted, someone else will have to take over your work. Unless what you do is very simple, it may be necessary for you to update a co-worker on what you're working on, so they can take over more smoothly. While we don't know exactly what your boss said, he may be expecting you to initiate this; failure to do so could affect future references.

As for people thinking negatively about you: I've worked in places where the opposite has been true when I announced my departure. Sometimes I've found that people thought more highly of me than I realized. Other times I heard things like "You got a job at {insert perceived great workplace here}? So cool! I'd love to work there. If they have another opening, please let me know."

Also, there's the human factor - people will want to say their good-byes; if you just up and leave, they are more likely to think negatively about you than if you give them some advance warning.