Performance

Kali is slow and inefficient witch is fine if you have a beefed up laptop but if your running on a laptop from 2013 every bit of performance matters.

Kali also installs a heap of unnecessary tools.

Daily driving

Whilst Kali is purely meant for pentesting, parrot also allows you to use your computer like a regular person.

Office suite

Kali comes with no preinstalled office suite however Parrot OS comes with Libre office preinstalled so you can write your reports.