Why is doing the wiring? If you are then put in two lines.
If it was an electician and they wanted alot more for a second line...

OR

You dont have enough space in your meter box then only put in one.

I personally used two lines in my bathroom. One
takes care of the lights (4 in the ceiling and 7 or 8 in the vanity)
and
also the exhaust fan.
The other is dedicated to JUST the outlet (20 amp gfci)

If you do the math its amazing how much power a simple hair dryer
can pull out of an outlet..... 110volts X 15amps = 1650 watts.
Many hair driers use more than that. (at least my wifes does) so
at 20 amps X 110volts we have 2200 watts.

It sucks if you have to do things over again down the road. I rather
just get it right once and forall.