Most WordPress caching plugins write pages to disk. That choice looks harmless until you need invalidation, cache variants, or a second server. Here is what changes when the page cache lives in Redis.
Four things a WooCommerce shop can do with MilliCache, each backed by a check you run on your own store: shared pages for shoppers with a cart, a checkout cached on purpose, orders that clear their own pages, one rule for every currency.
Edit one synced pattern and the only safe move for most caching setups is flushing the entire cache. Why shared block content breaks URL-based invalidation, and how cache flags answer the question no database query can.