why json is used with ajax code example

Example 1: how to set json type jquery ajax

$.ajax({
    type: "POST",
    contentType: "application/json",
    url: 'http://localhost:16329/Hello',
    data: { name: 'norm' },
    dataType: "json"
});

Example 2: how to set json type jquery ajax

$.ajax({
            type: "POST",
            url: siteRoot + "api/SpaceGame/AddPlayer",
            async: false,
            data: JSON.stringify({ Name: playersShip.name, Credits: playersShip.credits }),
            contentType: "application/json",
            complete: function (data) {
            console.log(data);
            wait = false;
        }
    });