The Boss ™ Katana-100 is a great sounding amp with a myriad of effects, amp models, and overdrive/distortion (OD/DS) settings, but configuring the ones you want to use, switching between them whilst performing, and tweaking settings on the fly is a real challenge.
This complexity is probably a barrier to someone considering moving away from a 'basic amp plus pedal board' rig to a Katana-only arrangement. The fact that the amp can only hold 8 patches (channels) in memory (only 4 patches for the Model 50) can also be a constraint.
Enter KatanaMan. It allows the flexibility and creativity associated with a huge range of effects, whilst providing almost unlimited patch storage, and simple one-click changing between sounds/songs (rather than the complex tap dance sometimes required with a pedal board !).
For a musician in a covers band, where just about every song requires a different sound, having the ability to single click/tap, to change from one sound/song to the next makes for a more consistent and professional performance.
Mounting an Android device on a microphone stand gives ready access to the amp's features and settings with a few clicks, as well as making patches and setlists simple to select. Here is a picture of a cheap 7" tablet mounted on a mic stand.
From experience 10", 8" and 7" tablets work well (especially if you have 'fat fingers' !) - although 4" and 5" phones are usable too - and make a good back-up device.