Im not sure, but it might have had some relevance in the format back in the day
Effects that modify or replace the cost to cast a spell (such as flashback or casting a spell without paying its mana cost due to suspend) don't affect the spell's mana value, so they won't change whether Lavinia's first ability restricts that spell from being cast
For example, if an effect copies a card in exile and allows you to cast the copy, casting that copy will cause Ghost-Spider's triggered ability to trigger
If you have a combo that never ends, then the game never progresses and is a draw
Radiant Destiny becomes an Always Watching, which was a great pairing with the exert mechanic (or any creature card really)
Vv'viza remains furious that the Uthros Combine is still entertaining information from Mm'menon, a contention that can likely be traced back to their longstanding rivalry from their days in the Administration branch