There are several benefits to owning a Weapons NFT opposed to crafting them which have been covered in detail on the NFT Integration page, but briefly include:
NO EXPIRY
Unlike the crafted variants of these weapons, Weapons NFTs NEVER expire.
BETTER STATS
Higher stats can be achieved using NFTs as both their minimum and maximum stats have been raised by 20% compared to those that can be crafted. Stats are completely random but the min/max bounds have been increased by 20%.
NO LIMIT TRADING
Crafted items can only be traded ONCE. Once they're traded, they cannot be relisted, even if they are unused by the buyer.
USABLE IN F2P and PFR
Unlike crafted items, all NFTs are usable in both FREE TO PLAY, and PLAY FOR REWARDS game modes.