Arrows and why they matter?

[Vogie]

Even if that were true, (And I don't remember any rules saying that you can only have one quiver ready) it would very unlikely for a quiver to get emptied in the middle of a combat

If you always start at 20. It's common to fire 3-5 shots/turn for any of the ranged classes, between extra attack and Crossbow expert's bonus action hand crossbow attack. Fighters have action surge & extra attack multipliers alongside various subclass features; Hunter Rangers have the Horde breaker & Volley features.

A level 15 Samurai with a Hand crossbow can take 5 attacks each turn without breaking a sweat, due to crossbow expert and Rapid Strike, for a total of 8 arrows fired in 6 seconds if they use action surge, and jumping to 10 arrows a turn at level 20.

A Volley from an 11th level hunter ranger can hit potentially 16 targets - provided they're all in a 20ft cube ("any number of creatures within 10 feet of a point you can see within your weapon’s range"), as a pair of 5 ft squares in all directions from a point. If they have Horde Breaker, and there's a target within 5 ft of a hit target that isn't in that zone... that grows it to 17 targets

1	2	3	4
5	6	7	8
9	10	11	12
13	14	15	16

And there's a discussion of the wording on Swift Quiver to contend with. RAW wording makes it sound like it's only providing free ammo for the 2 bonus action attacks, while others think it gives essentially free ammo for the duration.