swap-router-contracts vs. periphery contracts

[jpeer]

not a bug or feature request, just a question, namely: what is the problem that swap-router-contracts is solving compared to uniswap's already existing routers?

is it to provide a more convenient and possibly unified API?
is it to provide a more concise API, that is only concerned with swapping (and not liquidity providing)?
is it to safe gas, or solve some other technical issues with pure routers?

thanks in advance for any infos!