I sort of do a combination. I combine half fresh/ half frozen. I know milk doesn't spoil for several months in the freezer, but i don't like to keep anything older than a month or 2. because like others have said, the nutritional content changes to suit your growing baby.
You want your baby eating nutrient rich breastmilk, but it is also nice to have a bit of a stash just in case. I think combining gives you the best of both worlds. so on the days that i work, i freeze half of what i pump and keep the rest in the fridge for the next day.