Why do I need to specify a MEMO and in what cases?

Memo, Destination Tag, Payment_id, note or comment to the payment – this is an additional option of the address in the details, required to be filled in. This label serves as the identifier of the client who transfers funds to the address of the service or any platform. This payment note is used in those networks where it is provided by the mechanics of the network itself, such as Ripple, Binance chain, Stellar, Toncoin and others. When transferring funds to personal wallets, the label is not required. But if you are asked to specify it, then it must be done.