It does one thing: It indicates the author is willing to use "established patterns" instead of reinventing the wheel. (While sometimes it's good to reinvent the wheel - today's vehicles won't work with wodden wheels)
PSR is an abomination. You end-up with more blank lines than code and about 5 lines of doc comments to every line of code. Factor-in PHP's pseudo-Java verbosity and the actual business logic is drowning in a sea of boilerplate.