The Standard PHP Library (SPL) provides core PHP functionality like autoloading, exceptions, and file handling. However, its iterators and data structures may have limited relevance in PHP7 due to performance issues and the availability of alternatives like Rudi Theunissen's PHP7 data structures extension which offers faster and more memory efficient implementations of common data structures like stacks and queues. While SPL interfaces are still useful, many of its other components could be replaced by more optimized third party extensions for modern PHP applications.