It’s strategically advantageous to book 2 one ways if the price is the same (or even less sometimes). That way if you miss or need to change your outbound flight, the return flight is unaffected and won’t need repricing.
On the other hand, it is not a strategic advantage to have two one-ways if you decide you need to reschedule your trip. On a multi-city you would pay one change fee plus the fare difference. On two one-way tickets, each ticket would be subject to a change fee plus the fare difference.
There are various scenarios where a multi-city has advantages over two one-ways. There are also scenarios where two one-ways may be an advantage.