Best practice is a template or experience accumulated in previous BPM implementations. Any work can be started from a ground or by using an existing experience. As a rule, using previous experience is much more productive than starting from the ground. In this sense best practices in BPM can be considered as a sort of franchise and are very valuable.
However, as with any template, best practice is void without a gifted content filled into its placeholders as implementation. Here everything really depends on implementers. As with any practice or law, it can shine as a diamond in good hands and annihilate to complete degradation with ignorant followers.
Best practices are cornerstone of BPM describing essential metadata of the business. But their practical value entirely depends on the actual implementation data filled into these meta-models.