While I was looking to copy a sound effect for a texture pack in 1.15.json, I stumbled across the sound files smithing_table1, 2, and 3 and fletching_table1 and 2. I was sure those blocks didn't have any functionality yet, so I found their object files, imported them into Audacity, and sure enough, they were unique, unused sounds. While they're unused yet, there's a possibility they might not ever get used. I think I'm the first to discover this, but I might be wrong. I'm not allowed to post the actual sound files, but I have a description for each:
smithing_table1: Similar to the anvil repair sound, but dinky and high-pitched.
smithing_table2: A unique sound that might be a sword clashing or breaking.
smithing_table3: Similar to smithing_table1 but normally pitched.
fletching_table1: Again, similar to the anvil, but against wood and with the twang of a bow string.
fletching_table2: fletching_table1 but only the last two hits.
Now this is 100% speculation, but it might just indicate heavy and light swords/bows. Maybe light weapons are less damage but less cooldown, and vice versa for the heavy weapons. Who knows? These are exciting pieces of information, because it might say what is to come with a future or the current ongoing combat update/tests.
Here's an image of the sounds in audacity, if that helps at all: