Well, 'moderated' means you can hear your participants spoken-out-loud thoughts, while diving even deeper by asking them ad hoc questions in the heat of the moment.
And the joy of doing this 'remotely' is that you and your participant can do this from the comfort of your own homes in your respective favorite PJs. Although if you need a more sensible answer, we could go with - it saves money, time, resources, your most useful participants may not live in your area, you may not have the equipment you need, travel budget could be limited, we could go on...
This is why the ability to conduct remote moderated studies is so important - you get all the quality insights without anybody having to travel!