What sorts of uses do you have on a phone where a terminal is useful?
* rsync (backups, pulling audio files, pushing pictures)
* vim
* git/hg (all my notes live in a repo)
* random scripts (ex. When I was losing weight, I tracked calories with some shell scripts. I also have one that uses root and /system/bin/input to automate things.)
* youtube-dl
* python
* ssh for shell access
* socat + dynamic ssh port forwards
* access android APIs [1]
* general scripting, also using [1]+[2]
* backups (rsync, pigz)
* ffmpeg to transcode .mov to mp4 from a digital camera on the go
* openssl to debug stuff/inspect certs
* dig for checking dns
Half-jokes aside, keep in mind you can use small Bluetooth keyboards and get a micro-laptopish experience, or connect the phone to a monitor or TV and use a large Bluetooth keyboard to get a more desktop-like experience.
I imagine a terminal could work very well in those settings, if you need one.