Yes, the install will do all the partitioning for you. The point of
gparted is that you can use it to partition and format any extra disks
you might add to your system - you cannot use it to partition the system
itself as it will only work on unmounted disks and you cannot unmount
the running system.

Personally, I find it very useful, but then I deal with quite a large
number of USB hard disks. I doubt that most people would have any need
for it