I've got one T430s that dual boots between Windows and Fedora, and Fedora is fine with the Secure Boot on (if you use your custom kernel modules, you will have to sign them, though). Windows, on the other hand, can be annoying when the Secure Boot is off.
Ubuntu nags you to do it so it can run 3rd party drivers. It's never really explained what the drivers were and I haven't noticed any difference with it disabled or not
Fedora and RHEL won't load any unsigned kernel module (yes, found out the hard way: I was wondering why VirtualBox doesn't run, even if it successfully builds it's own modules). However, you can enroll a MOK (Machine Owner Key) and sign whatever you want.
I was under impression, that Ubuntu does not enforce signing kernel modules even with Secure Boot on.
I've got one T430s that dual boots between Windows and Fedora, and Fedora is fine with the Secure Boot on (if you use your custom kernel modules, you will have to sign them, though). Windows, on the other hand, can be annoying when the Secure Boot is off.