A permit protects the homeowner and the future occupants. If a professional suggests that you do not need one, check with the building department yourself, as this suggestion is usually a red flag that your contractor or architect are trying to cut corners.
It is always to your advantage to get a permit. A permit ensures oversight of the work. The scrutiny of an inspector can guard against mistakes and shoddy workmanship and ensure that the work adheres to building codes.
A permit will also help you avoid headaches in the future. If building officials discover you have done work without a permit, you could be required to dismantle your remodel and start over again. If you sell your house, you might be legally obligated to disclose that you have remodeled without a permit, and the buyer could demand that you bring work up to code.
Some things you need a permit for:
Change the footprint of your house
Replace an electric stove with a natural-gas model
Move a load-bearing wall
Install new electrical wiring
Create a new door or window opening
Move a sink
source: Home Tips