The purpose of the PSRs is to help support and foster collaboration between members of the Framework Interoperability Group (the people who draft and publish the PSRs: consists of medium-to-large PHP projects including Symfony, Amazon, Drupal, Joomla, etc.). Having a common coding standard makes it much easier to publish code as part of other PSRs as questions like "tabs or spaces?" don't have to get rehashed every time a new PSR is drafted.
That's to say PSR-2 is not intended to a be a "best practices" type of thing: it's actually just the result of a survey of member projects at the time with each part chosen because that's what the majority of them did, even if it was just a simple majority or there were member projects were with the majority on, say, tabs vs. spaces but not, say, indentation size. Some of the FIG member projects have adopted it, but several haven't and don't intend to. It's useful if you don't have any other coding standard available, but easily ignored with no loss of interoperability with the other PSRs if you do.
That's to say PSR-2 is not intended to a be a "best practices" type of thing: it's actually just the result of a survey of member projects at the time with each part chosen because that's what the majority of them did, even if it was just a simple majority or there were member projects were with the majority on, say, tabs vs. spaces but not, say, indentation size. Some of the FIG member projects have adopted it, but several haven't and don't intend to. It's useful if you don't have any other coding standard available, but easily ignored with no loss of interoperability with the other PSRs if you do.