As was pointed out in VazkiiMods/Quark#4648, the "whitelist" / "blacklist" parameters to RecipeCrawlHandler are not terribly useful:

• The whitelist parameter can be emulated by performing a normal recipe crawl, then adding any additional desired items.
• The blacklist parameter can be emulated by performing a normal recipe crawl, then removing any undesired items.

The whitelist/blacklist parameters do not meaningfully affect the recursive parts of the recipe crawl algorithm, all it really does is call massRegistryGet on your behalf.

Especially in the case of Quark's Magnet System, usage of the whitelist/blacklist parameters creates a situation where you need to enter item IDs, but you really mean to enter block IDs.

I'm not sure im understanding this right but one use of having a whitelist that affects the recipe crawl is to remove certain items derivated from others. For example having the recipe crawl remove blacklisted stuff like tripwire would fix blocks like shulker boxes and trapped chests from being considered magnetic