Boot Arguments are specific configuration flags passed to the kernel on boot. Every kernel has certain arguments it accepts and the values of these flags can be changed.
In general, it isn't safe to remove or change the default arguments if you aren't sure what you're doing, as the device and UI features may no longer work correctly.
For Android devices, Linux kernel command-line parameters are documented here.
For iOS, the default boot arguments are:
-v debug=0x14e serial=3 gpu=0 ioasm_behavior=0 -vm_compressor_wk_sw
Vendor devices may offer other undocumented command-line parameters.
To customize your boot arguments, simply head to Settings and modify the appropriate text field.