With level squish coming to Shadowlands, I admit I wasn’t overly impressed with World of Warcraft doing a month-long double experience event. However, the event they are starting on Monday, April 20th, is much more appealing to me as someone who was unsubscribed for a large chunk of Battle for Azeroth.
Impressive Influence will grant 100% bonus experience with the factions of Legion and Battle from Azeroth (although it does exclude the two newest factions, Rajani and Uldum Accord). This is a great buff if, like me, you haven’t finished up your Battle for Azeroth or Legion Pathfinder achievements, or even if you’re the type inclined to farm up a bunch of paragon rewards.
Be aware, however, that reputation requirements for Allied Races are going away with Shadowlands, so unless you really want to level another character now (and why would you with the much more compact leveling experience on the way?), these rep grinds won’t be necessary.
ETA: Blizzard has also announced that they will be keeping Winds of Wisdom – the experience buff – live until Shadowlands pre-patch for players of Battle for Azeroth.