A few things , first off always pull the permits. The cost now saves you much more down the road. If yo aren't sure if you need a permit for the work being done, just call the local building office and ask, they are generally helpful and nice to people trying to do the right thing.
Second try not to upset the building/zoning officials as they can make your life extremely rough in future endeavors, and another point to that they can also be some of your best team members when locating future properties. If they know you're legit they are dealing with houses all the time all day every day they typically know the back story of many local houses and can be instrumental at finding you potential leads and also if you really get a good relationship with you they can give you loads of advice and tips. My mentor has a team member that is a building inspector for a town he invests in and he has taken him with him (off the record) on first visits when he does his initial walkthrough to give him an idea of what will need to be upgraded, what better way to figure rehab costs if you know from the get go what has to be done.
Third, realize that as much as EVERYONE hates the inspectors they're just doing their jobs. Part of their job (especially if you're not doing the work yourself) is to make sure the contractors are doing an adequate and proper job and not cutting corners or taking advantage of an absent or unsavvy owner.
Also know that sometimes if they find out you have completed work that requires a permit without obtaining one they can make you go back and show the work in the various stages they would have inspected it which means basically redoing the work all over again at 100% out of pocket cost to you, plus they will make you pay the permit fee and most likely will hit you with some fairly hefty fines. Example: if you decided to redo the entire interior of the house and its all completed and they find out you did so without the proper permits because they see the contractors leaving the job site after you just handed them their payment, you may get a knock at the door and well because after rough framing (before drywall is installed) they would normally inspect the plumbing and electrical you had all redone, guess what you will have to remove all the drywall so the can look at what they want to see.
It is always just easier to do the job right the first time part of the job is pulling the proper permits.
@Joe A. and @Bruce Woodruff I don't know about all areas but where I am the permit must be displayed and viewable from the exterior of the house without obstruction at all times while the property is under construction (most people place them in a front window of the building).