As Davide said, start-shell gives you possibility of root access on the underlying linux Kernel. Some support commands might be provided from time to time in this blog to help deep troubleshooting that would be conducted by Aruba support. The CLI development aims to provide all the in-depth command as well (like diag command). Note that in ServiceOS there is the secure mode setting that prevents access to start-shell if desired. Changing this mode requires zeroization. The swtich by default is set with secure mode being standard (with start-shell access enabled). With enhanced setting, start-shell won't be allowed.
SVOS> secure-mode enhanced
############################WARNING############################
This will set the switch into enhanced secure mode. Before
enhanced secure mode is enabled, the switch must securely erase
all customer data and reset the switch to factory defaults.
This will initiate a reboot and render the switch unavailable
until the zeroization is complete.
############################WARNING############################
Continue (y/n)?
If you have very specific points where you think start-shell is required, do not hesitate to raise them.
I hope this helps.