Deprecation is a stage of partial support prior to the next stage, which provides no support at all. During the period of deprecation, PHP Code still works, but superior code exists to take its place in the new language version. This is an overlapping in time allowing programmers to learn new aspects of the PHP language and to replace old PHP code with new PHP code.
If PHP Programmers fail to learn new versions of the PHP Language, they fall behind… the result being a deprecated web site. If left unchecked and the web server is updated to the current PHP version, the deprecated website may stop working altogether.