Discuss the 'v-memo' directive introduced in Vue 3.2.

v-memo caches a sub-tree of the template and skips updates unless specific dependencies change.

This is a micro-optimization directive. It takes an array of dependencies. If the dependencies are the same as the last render, Vue skips the VNode creation and the diffing process for that entire sub-tree. This is extremely effective in large v-for lists where only a few items update at a time.