By best practice collections are typically instantiated in a Block. Best practice also dictates that a Block should set a cache tag and lifetime to take advantage of the Block caching mechanism.
This practice may render the use of a collection cache somewhat useless, at least as far as front-end performance is concerned. However the Collection Cache in Magento is ONLY utilized in TWO areas: neither are guarded by a Block cache: the Website collection (from within Mage::app()) and the Mage_Sales_Model_Resource_Order_Item collection.
This much makes sense. Lots of load on these collections from various places within Magento - it makes sense to implement the cache.
So, my question is: does it ever make sense for me to implement a collection cache if the only place it is used is inside of a Block, and that block does not have wide reuse across the front-end? Any rationale as to best practice here would be welcome.
Typed from my phone, apologies for typos