It depends. If you need a faucet changed out with this new fancy one, or if you want to replace a toilet with a new one using less GPF, or any other kind of update/remodel.

Not every job a plumber does is an emergency situation. I used a plumber to help me setup a backyard project to set up a portable propane tankless gas water heater. I took a look at buying at the parts and pieces I would need, but they needed special tools that would only be used once if I were to buy them. Instead, I had the plumber do it for me with all of the necessary parts/pieces on the truck plus the tools to do it. It cost me less than it would have to buy everything. Now, I just need a cold water feed, and I have a portable hot/cold running system.

Exactly. For example, we replaced a couple of toilets and wasn't that urgent. So we called him and he gave us an appointment after a week.