The main benefit is that it allows us to change how we vote for President over time without requiring a Constitutional amendment every time. This is because the states themselves can decide how they select electors, and can try out different voting systems without requiring permission from the federal government.

For example, there is currently an agreement between states that, if they get enough states to agree for a majority of electoral votes, they will all switch to using the national popular vote as their only criterion. So we can switch to that system with less than half the states, rather than requiring 3/4 of them to approve an amendment. And of we decide we hate the system later, we can switch back, again without an amendment.