This kinda wack advice is the difference between career minded people and job minded people.
If you are in your career you need to give that two week professional courtesy. It will get around eventually that you don't if you don't and you'll find it harder to get interviews after a while.
And this is coming from someone who has held management positions.
Coming from someone who is currently in a management position professional courtesy is not as important if your NEXT job is willing to make an offer
If they want you to start immediately you tell them you can start immediately (if you want the job). If you leave job A for job B and then down the line try to move up again to job C, job C isn't going to contact job A about "how you left them" if you build a positive work history at Job B (years good track record etc.)
I've interviewed (this year) people who said that they needed "time to consider" if we offered them the job and immediately

them as a prospect. Hired a guy on my team currently who said that this job was exactly what he wanted to do and that he wants to start the job yesterday.