Hail and well met! 

I’m a bit behind on topics but wanted to throw out my most frequently used house rule.  I don’t know why, but in each of the three groups I’ve played recently, the player who most wants to use high magic is also the player who can’t add up their dice quickly. Without fail, they’d fire off some big spell, altering reality and potentially tearing the mask of God, but then start counting on their fingers as they add up the damage dice  Or, god forbid, roll their 12d8 but they only have a single d8 die, so they roll it 12 times, adding as they go (and sometimes forgetting if this was the 8th or 9th roll). Cue audio of a record scratch. I try to keep a cinematic and high energy pace, and nobody wants to go out for a thrilling evening of watching some dingus add single digit numbers together out loud.

To solve this problem, I habitually offer average damage for any rolls with more than two dice. A 5E fireball is 8d6, average of 28. This lines up with the 5E monster manual, which presents average damage for monster attacks, breath weapons, and the like. I also use this house rule with healing potions, especially if they’re chugging 3 or 4 after combat. 2d4+2 averages 7, so four potions is 28.  Some players can add dice quickly! If they want to draw it out a little, rolling fistfuls of dice, they still can. But sometimes the pace at the table is better served by taking the average and moving along.

Hope all is well,

Joshua