If it is something minor (which would probably irritate the inspector to come and look at with *me* doing the work), and something I know 100% that I am doing to code and safely, then no.
But say I am just adding a new electrical switch... Well I used to be an electrician, so I know what I'm doing and don't cut corners. I *don't* use whatever wire happens to be in my shed. If I don't have the proper wire, I go buy it. Same with electrical box, switch, grounding, and everything else related to the work.
So if I am out of some wiring supplies, I will go spend $20 or $30 to get the right stuff to add that one electrical switch. But then I'll probably get a roll of wire and a box of wire nuts which I will use on other projects.
And I usually ask for permits more than is necessary. I'll ask if I need a permit for this or that, and sometimes they say that I don't need a permit.
And when I do get a permit for say electrical work, the inspector looks at some of my work, but not everything. He sees that I am doing things to code where he looks, and figures everything else is the same - which it is. And these guys are busy, they don't have time to look at everything (unless they can see that there are a lot of code violations), so it is really up to me to be sure all my work is done to code and is safe.
At one time, the inspector lived across the street from me. I was doing some work on my front porch and went to his office to ask if I needed a permit. He said don't bother. But basically I had the benefit of having a permit, because he drove by my house and saw what I was doing every day. So if I did anything which was not up to code, he would have pointed it out to me with a quickness. Actually when I was done, he came over and said nice job, and that I went beyond what code required!
I just installed a woodstove, hearth, and chimney. I had *no* idea what I was doing before starting this project. So you bet your bippy I got a permit. But I also read all I could about it and went to ask the inspector questions a few times before doing the work. So I now know 100% my work was done properly and is safe. The inspector came out and inspected everything and said nice job. (Double-checked my work.) And my insurance guy came out and inspected my work as well. (Triple check!)
So I would say, if you're *not* 100% sure what you are doing is safe and up to code, then get a permit - even if it is adding just one electrical switch. And so what if the inspector asks you to re-do some work, well you have learned something and will know your work is done safely. You will sleep better at night.