The subject could be seen as very complex but for most use-cases there is a simple litmus test. Do you need censorship-resistant transactions or a neutral/decentralized timestamping server? If not, then you don't need a blockchain. That's really it.

In the case of a vendor, accepting _bitcoin_ has own security advantages, and bitcoin comes with its own blockchain built-in. As a vendor you probably wouldn't really need to worry about the blockchain as much as you would need to worry about avoiding exchange rate fees.