I've done it with certain foods when trying to determine intolerance and negative side effects (reflux, nausea, cramps, etc) under the recommendation of my doctor. I cut out all dairy, gluten, eggs, soy, caffeine, citrus fruits, and all juices. I ate only at home for 3 weeks and checked all the labels to ensure I wasn't eating or drinking anything I wasn't supposed to. I was pretty sure soy and gluten weren't the culprits so I introduced gluten back first at the 3 week mark, and soy at 4 weeks. With each re-introduced food, I tried to eat it daily for a week. If there was no repeat of the side effects, I introduced another food after a week. If there were, I stopped eating it and waited for the symptoms to resolve (usually within about a week), before reintroducing anything else. After soy, I did eggs and had some symptoms so had to stop eating that and wait a little while before moving on to caffeine, then citrus, then juice, then dairy, all of which I had issues with, as I expected I would.
I kept a journal of everything I ate during the time and made notes of how I was feeling along the way. I think when it comes to reintroducing foods it's best to go in order of the ones you think are the least likely to cause issues first.
Overall, the whole trial for me lasted about 2.5 months or so, largely because of the number of foods we tried and how many I had issues with during the trial. I was pretty sure of how everything was going to play out, but it did give me a better idea of how specifically each food affects me and how much I can have before experiencing side effects. Since a lot of these were foods that I tended to limit or in some cases eliminate completely before the elimination diet, for me I didn't have any huge change in how I felt afterwards, but did have a better understanding of how I feel when I eat certain things. It also helped to give my doctor a better understanding of how much (or little in some cases) impact each food has on my overall symptoms so that my care and medicines can be prescribed more efficiently.