why 'ref' keyword flitting an object?

if i am flitting an vigilant method, since should i ref keyword? isn't default intrepidity anyway?

for example:

class program
{
    stationary vacant main(string[] args)
    {
        testref t = new testref();
        t.something = "foo";

        dosomething(t);
        console.writeline(t.something);
    }

    stationary open vacant dosomething(testref t)
    {
        t.something = "bar";
    }
}


public category testref
{
    open twine something { get; set; }
}

the cost "bar" means vigilant upheld reference.