Why not Store Your NFT Assets Online?
Storing any file in the cloud (eg AWS) or on one's web server is a centralized storage model. Centralization refers to the fact that one entity or person controls all aspects of storage, including access and maintenance.
Keep in mind that the NFT is not the actual image or video file associated with the artwork, but rather a token containing a link indicating where the work is stored.
If the artwork itself is stored on someone's web server and that person decides to shut down the server or change another image, the NFTs may point to a file that doesn't exist or is different (not a collector's purchased artwork)). The collector has no control over the fate of his NFT in this scenario.
While storing files on services like AWS seems less risky, NFT owners still rely on third parties that pay AWS storage fees to manage files. If the person responsible for paying this fee does not do so, the files you saved may be lost.
There have been a number of cases where the NFT market went out of business and left storage costs unpaid with the result that a large number of NFT work files were lost.
With IPFS, anyone with the exact original graphics file can be sure that NFT references it, guaranteeing the value and integrity of the NFT.
What does it mean to say your NFT is kept "On Chain" versus "Off Chain"?
In rare cases, one could actually say that the NFT is stored entirely on the blockchain ("on the chain"), as with NFTs generated by small code snippets like autographs. However, the artwork associated with most NFTs is stored off-chain, typically on servers that use the IPFS protocol or on centralized servers such as AWS.