Correct, it's not needed initially. You have 8GB of internal storage, which is plenty to hold either the full NAM or European map. As noted above, "However, you're safe with 8GB internal for one map of either North America or Europe for a while, so even an 8GB card would be enough for the other map.
And UNLESS you really need to hold them both in the unit at the same time, MyDrive allows you to swap them back and forth off your computer if you have purchased the 2nd map already. These days, TomTom knows the maps to which you are entitled, and MyDrive lets you flop them back and forth at will if necessary. Takes a while to unload/load them onto the unit, but it's one approach...