The main disadvantage of MVCC is the background work necessary to clean up its visibility data and keep disk space under control, the topic of the next section.
You should also be aware that MVCC cannot make all possible concerns about interactions between sessions and ordering magically go away. In fact, not seeing data another session has been altering until later can introduce its own new class of problem, for applications that are used to traditional locking approaches. You've seen how the UPDATE and DELETE order might happen in an unexpected way with a regular Read Committed MVCC session, and you can't just make these go away with serializable without preparing for some transactions to fail badly too.
