Running a website takes a lot of time, especially when each post requires a picture that is related to it. The reason that pictures are important is that it helps with the on-page search engine optimization, improve that, and the page is likely to rank well. The problem with pictures though is finding them. Unless the web developer has a lot of photos they have taken themselves, then they need to find what they are looking for somewhere online. This is where stock photos come in handy, as they save a lot of time worrying about copyright issues, and they make finding relevant photos easy.
One thing that troubles a lot of people who use pictures on a website is the issue with copyright. It is no longer a good idea to just go to a search engine to look for a relevant image and use it. This can lead to all kinds of legal issues in the future. The good news is that thanks to the sites that supply stock photos, these copyright issues do not exist, as long as the license agreement on the site is adhered to. In some cases a small attribute back to the photographer is required somewhere on the page, or if the rights have been paid for, then no attribute is required.
The benefits from using a site that has lots of photographs in stock is that only one source is needed. There is no longer any need to go searching for pictures, as they can all be found in the one place. This can save a lot of time, and for web developers, time is money. So, whenever a picture of a particular location is required, or maybe one of a specific object, then a site that holds stock images is the best place to go.