Do I need ETH to swap?

Could you please clarify, do I absolutely require ETH to carry out a swap transaction? Or are there alternative cryptocurrencies that could be utilized for this purpose? If ETH is indeed necessary, what are the reasons behind this requirement? Is it due to the popularity of the Ethereum network, its scalability, or perhaps some other technical aspect? Also, could you elaborate on any potential drawbacks or limitations that might arise if I choose not to use ETH for the swap? I'm trying to make an informed decision and your expert insight would be greatly appreciated.