Normally when working on a modpack you install very nice mods. But let's say you're working on a modpack, or transferring mods to another modpack of the same game. When you click on one of your 'Modpacks', go to 'Mods' and click on one of the mods in the 'Mod List' there should be a button to instantly install that mod to another modpack.

How it is right now, is if you want to install a mod to another modpack, you have to read the mod in your mod list, search it up, find it, and then install it. If you repeat this process for hundreds of mods you will quickly learn why this feature is needed, not just recommended.