Normally Termux does not require device to be rooted. In fact it's primarily targeted for non-root users.
You may want to root your device to:
- Modify a device's firmware.
- Manipulate the parameters of the operating system or kernel.
- Non-interactively install/uninstall APKs.
- Have full R/W access to all file systems on device.
- Have direct access to hardware devices such as BT/Wi-Fi modules or serial lines.
- Install a Linux distribution on top of Android through chroot (not proot!) or containerization.
- Generally have "full" control over your device.
Otherwise root isn't necessary.