Hard drive selection

One of the areas you don't want to cut corners on when choosing a system for Kali is that of the hard drive. It is usually a good idea to get a drive that has at least 150 GB of space, but you should consider drives larger than this if possible, as you will undoubtedly install other tools that aren't included in Kali (not to mention the data you generate will take up space as well).

Keep in mind that, as a penetration tester, you will be not just asked, but required to keep your findings confidential and, for many tests, this means wiping the hard drive to be safe. While it is possible to clean an installed OS so it is returned to its base or original unaltered state, you still may want to wipe the drive. The suggestion would be to set up the system the way you desire then image it so you can effectively wipe a drive then restore your original image at will. Always keep in mind that losing control of or leaking information is something that will not only upset your client, but open you up to lawsuits, loss of reputation, loss of career, and bad karma. Basically, take the proper precautions with the data you have gathered both during and after a test.

When I acquired my current Kali system, one of the first things I did was to replace the hard drive with a larger SSD drive. I feel that this investment is a good one for many reasons which I will try to explain here.
First, the use of an SSD drive will typically result in the reduction of battery drain on a system to some degree. This reduction in battery drain results in longer mobile use when you can't plug into a wall.
Second, SSD drives are faster than traditional hard drives by a substantial amount. SSD drives result in faster read and write times than a traditional hard drive. Being able to retrieve and manipulate data faster is a tremendous benefit for a penetration tester (or anyone for that matter).
Lastly, SSD drives can take a lot more of a beating than older traditional drives. The lack of a spinning disk inside the computer means that moving and transporting the drive plus system is a lot less likely to result in drive failure.
These are the things I considered when moving to a solid-state and I don't feel like I made a bad choice.