You can judge whether you need to reboot based on the CVEs being patched. Some things probably don't apply to your situation but the system tells you to reboot because it doesn't know. You can see them here: http://www.ubuntu.com/usn/
Hopefully rebooting for Kernel patches will go away by the next LTS, which should be well into the 4.x Kernel and therefore able to take advantage of the new rebootless shim updates.
Hopefully rebooting for Kernel patches will go away by the next LTS, which should be well into the 4.x Kernel and therefore able to take advantage of the new rebootless shim updates.