Remarketing campaigns are usually a good idea… but not always.
I had a client selling replacement parts for power tools. A remarketing campaign in that case was useless because they normally want the part they need quickly so they can get on with their work. Once they bought it (from you hopefully), a remarketing campaign has no effect since they have their part, it would just be a waste. A taxi service also comes to mind, limo and locksmith as well.
On the other hand, I had a magician client for weddings, kids parties, corporate. Typically, there’s a longer sales cycle. They are researching and are not in a hurry usually as the event may be in a month or more. That’s a good time to remind them with remarketing. How often to do so depends on the sales cycle for that particular product. I had another client selling a $50-100k piece of equipment and clients would take 6-12 months before buying for various reasons. A chiropractor may remarket for just a few days since the potential client may be in pain and wants relief fast. He may not need to remarket for that reason, especially if he has a good sales page and clients choose him right away.