Finding a third party API is like finding a good parking spot near work, it may take a bit of time looking but once you find it, it saves you time and money. A third party API is developed external to the user. What this essentially means is that a company building their API can outsource other systems and client libraries to use for their own system. Think of a jigsaw puzzle, you can either build the pieces and put them together or you can go to a third party API, take their jigsaw pieces and put it all together.
The first strength associated with third party API's is the ability to utilise the external developers expertise. If an API is already providing reliable information then you can effectively utilise that information instead of populating it yourself. For example, if you are developing an application relating to medical conditions, then you would have to populate it with numerous medical conditions, which requires a certain level of expertise. If there is a third party API available then you can simply take the pre-existing client library saving you from sourcing a medical expert to use within your application. Additionally, developing this part of your application may not fit into the core function of your business which can somewhat stretch the focus of your company.
Probably the most obvious benefit associated with third party API's is the saving of time and money. The cost of coordinating and developing in house can be quite excessive, especially when you're building an entire framework from scratch. When you use a third party API you pay the license fee, address security concerns and integrate it into your system. The upfront cost associated with the license agreement can seem excessive at the time but when you compare that with the cost of employing in house developers, the cost seems quite reasonable. This was hinted at previously but the time spent on employees developing and populating information detracts them from the business' core focus. As a result, the business loses key personnel for a considerable amount of time " adding to the costs of the project.
As a developer, there is nothing worse than starting from scratch. It's the equivalent of taking the longest route to get to your destination when there is a clear shortcut available. Hence, I thoroughly recommend using a third party API or multiple third party API's when developing your system.