Just an example of what justifies the need:
4,423 songs installed at 128kbps of over 5800 on my Macbook at higher bitrates. Years ago I moved the entire collection into iTunes, I obviously don't listen to all of it every day, but I like having the convenience of my entire music collection whenever I want to.
90 Apps installed of 115
1,746 Photos, nice to have an album of many many photos I have taken and saved over the years readily available at the touch and swipe of the screen 😀
7 Videos recorded, 48 videos sitting in my computer, some of them I would love to have in my iPhone.
This leaves me with currently less than 1 GB free on my 32GB iPhone, and this is after removing a few albums last night during a backup synch.
I have been utililizing iPods for 9 years. You tend to build up needs for capacity and depend on it over the years. As capacity becomes available, the need to utilize it becomes important.