When to use "rereduce" in a custom reduce?

Couchbase Server
1

Hello,

i’m trying to create a custom reduce and I’m a little bit puzzled on when to check rereduce.

I have a very simple map for my test.

function (doc, meta) {
    if (doc.type === 'doc') {
       emit(doc.user, doc.date); 
   }
}

And this is my reduce


function (key, values, rereduce) {
    
    var latest = null;
    for (var i = 0; i<values.length; i++) {
        if (latest === null) {
            latest = values[i];
        } else {
            if (latest < values[i]) {
                latest = values[i];
            }
        }
    }

    return latest;

}

Basically, this reduce outputs user’s last post date.

In this particular reduce, when should I use rereduce?