As I know, Swap is to change the token or the blockchain of that token. Thus, there will be a number of swap token cases as follows:
+A project issues ERC-20 tokens on the Ethereum blockchain, then they successfully self-develop another blockchain and swap from Ethereum blockchain to their mainnet. For example: Credits, CyberMiles, Universa ... => They will become independent blockchains with their own tokens possessing many advantages.
+A project is using ABC token but then decide to convert it to BCD, they will swap, for example token SPARTA to ALTT => Increase token friendliness and consistency.
+A project token is allowed to exist on many different blockchain platforms. Like USDT exists on both Ethereum & TRON => The token reaches more potential users