I'm trying to determine the uses/purpose of the defaultconfigs folder as I run a server and have been unable to find anything on this. I realize it may be to terminology or just no one asking before.

The configs/files in defaultconfigs (or the folder that is set in configs/fml.toml) will be copied to the serverconfigs folder of any newly created world.

This is most likely for use by modpack developers, so they can setup the server configs they want to load every time a world is made in singleplayer.

Finally thank you, I have been looking for months what this folder is for. And on top of that it is just what I needed, I was tired of copying and pasting the settings in each world.

I also wonder what the scripts folder is for.

Sorry, looks like I have a bit of a delayed reply but the scripts folder is for a mod called CraftTweaker, which allows you to change crafting recopies, smelting times, etc. Nearly any professional modpack will be using this mod. More specifically, the scripts folder holds .zs scripts (CraftTweaker's own language) that let you modify the game. More information can be found in the CraftTweaker docs: https://docs.blamejared.com/1.16/en/getting_started/

 

For example, because I don't like Netherite, I might make a script like the following (I actually run this one on my server): 

furnace.removeRecipe(<item:minecraft:netherite_scrap>); //Makes it so Netherite Scrap can't be created by Ancient Debris in a furnace
blastFurnace.removeRecipe(<item:minecraft:netherite_scrap>); //Makes it so Netherite Scrap can't be created by Ancient Debris in a blast furnace
mods.jei.JEI.hideItem(<item:minecraft:netherite_scrap>); //Hides Netherite Scrap from JEI
craftingTable.removeByName("minecraft:netherite_ingot"); //Removes a specific recipe from the game. In this case, removes the recipe that turns scrap and gold into ingots
craftingTable.addShaped("EasyNetherite", <item:minecraft:netherite_ingot> * 2, [[<item:minecraft:air>, <item:minecraft:coal>, <item:minecraft:air>],[<item:minecraft:diamond>,<item:minecraft:obsidian>,<item:minecraft:gold_ingot>],[<item:minecraft:air>,<item:minecraft:netherrack>,<item:minecraft:air>]]); //Adds a new recipe that makes two netherite from coal, doamond, obsidian, gold, and netherrack.

The basics for the language are quite if you spend a bit of time looking at the docs. Hope this helps to answer your question!