Who gives referral code?

Could you clarify who exactly is responsible for providing referral codes in the context of cryptocurrency or finance? Are they issued by exchanges, wallets, or perhaps by individual traders looking to incentivize new users? Additionally, how do these referral codes typically work, and what benefits do they offer both the referrer and the person being referred? It's essential to understand the mechanics behind referral programs in the crypto space to make the most of these opportunities.