This is a mod aimed at improving performance of all crafting-related functions. It fixes the bug introduced in Minecraft 1.12 where shift-click crafting a stack of items could cause momentary freezes. However, it does slightly more than just fixing that issue.
FastWorkbench causes all crafting operations to cache the last recipe used. On top of this, it reduces calls to that cached recipe, by only detecting changes when the stored item in the crafting matrix actually changes (vanilla retries every time anything changes, such as stack size). This results in the number of matching operations being reduced to one, instead of anywhere between one and nearly 600.
FastWorkbench also removes the recipe book. However, it is far more sophisticated than mods such as No Recipe Book that only remove the book on the client. FastWorkbench removes the recipe book on both sides (server + client) at the earliest possible point. This results in faster logins, less wasted network traffic, and overall performance improvements due to recipe book functions being disabled entirely.
The no-op version of the recipe book invalidates the recipe unlocked trigger for advancements.
Compatibility and Mod Support
These changes only apply in a vanilla workbench, and as of 1.16, the player inventory. Other mods should be caching recipes for performance reasons on their own.
Be sure to also check out Toast Control!