You can figure this sort of question out. Let the ambient temperature
be 60 degrees F, a hot water temperature of 130 degrees. That means
you lose 48 Btu/ft-hr of 3/4" bare copper. 7 feet of pipe would be 336
Btu/hr. If you ran your hot water for 1 hour per day that would be
122724 Btu/yr or about as much energy as is in a gallon of gasoline per
year tops (unless this section of pipe stays hot while you are not
running the hot water at the tap).

I would think the "bottom line" is that pipe insulation doesn't make all
that much difference. It reduces the time needed to get hot water,
reduces the indidental heating of non-living areas. In the summer, it
might reduce slightly the load on the air conditioner. You insulate if it's
easy but don't get concerned if you can't.

Folks should know that insulation by itself will NOT keep even a hot water
pipe from freezing if you aren't drawing water and the pipes pass through an
un-conditioned area.