What requires a plumbing permit
The easiest answer to this question, is just to call your local municipality and ask if the work your planning will require you to draw a permit. Every municipality has different rules and if your caught doing the work without a permit you may be fined.
Plumbing permits are not there to be a burden on you but rather to protect you from unsafe building practices. Even if you decide to hire someone to do the work you should still be aware of the requirements for a permit.
Most municipalities will allow homeowners to do there own work but will expect you to have a plan and may require drawings before they issue a permit.
Any addition to your plumbing system or renovation of it will require a plumbing permit.
A repair to an existing system using like materials and sizes will not usually require a plumbing permit.
Here is an example of the required information.