The importance that cache block setup and tuning has on site's performance is a subject that most site implementers don't take into account early in the development process.
Often happens that, only when the sites are deployed and start to grow (both in size and concurrency accesses), maintenance crews experience the results of a rapidly and overwhelming increase of temporary and cache files being stored.
Sort of, in contradiction to what would be expected, moving the site into a clustering environment, might not solve performance issues related to these cache-blocks. (Quite the opposite will happen most times)

My suggestion is that the documentation is improved in order to raise awareness to the implications of choosing the best suited set of keys and cache block configuration.
In my opinion the documented alert should be referred in one (or all) of the sections:
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Features/Clustering
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Features/Clustering/Maintenance
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Reference/Template-functions/Miscellaneous/cache-block