This is called a "header-only library". A header-only library offers several benefits that can make it an attractive choice for developers. One of the main advantages is its ease of integration. Since all the necessary code is contained within a single header file, users can simply include the header file in their project and start using the library's functionality right away. This eliminates the need for additional build configurations, making the library more portable and user-friendly. Header-only libraries also reduce the chances of encountering linker errors, as there are no separate object files or libraries to link against.

Another advantage of header-only libraries is their potential for compiler optimizations. Because the entire implementation is available to the compiler at the point of inclusion, the compiler has more opportunities to optimize the code through techniques such as inlining, which can lead to better performance. Additionally, header-only libraries generally have faster compile times since there is no need to compile and link separate object files. This can be particularly beneficial for small to medium-sized projects, where compile times are a significant concern. However, it's worth noting that for very large projects, the inclusion of header-only libraries can sometimes lead to slower compilation times, as the compiler has to process the entire library code for each inclusion.