There is no need to.

I guess my question would be, is there a benefit or detriment?

Benefits: It will contribute organic matter to your soil. It will add iron to your soil.
Detriments: None really, except the smell. The nitrogen it supplies is very slow acting, so it probably won't cause excessive top growth when you don't want it in the summer. If you do add it, I would stick to the lower rate, 5-10 lbs per 1000 square feet, but I know people who add it all summer with no ill effects.

thanks tiemco, my lawn looks really good right now and the only thing different from last year is the milorganite. every other fescue lawn in my community is pale green and mine is a nice dark green. i usually do not fert after mid april.

Being an organic fertilizer you can apply it every day of the year if you can stand it. It will not burn in normal doses. It will have a fragrance however.