Why does DateTime to Unix time use a double instead of an integer?

Question

I'm needing to convert a DateTime to a Unix timestamp. So I googled it looking for some example code

In just about all the results I see, they use double as the return for such a function, even when explicitly using floor to convert it to an integer. Unix timestamps are always integers. So what problem is there with using either long or int instead of double?

static double ConvertToUnixTimestamp(DateTime date)
{
    DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
    TimeSpan diff = date - origin;
    return Math.Floor(diff.TotalSeconds);
}

Answer 1

To avoid the 2038 bug on 32 bit systems?