Hi
Can anyone tell me whether it is necessary, or even recommended to disable Secure Boot in UEFI before doing a fresh Ubuntu installation?

Ditto for CSM or Legacy Boot(BIOS) mode.

I leave both untouched from their defaults(enabled) and only disabled Fast Boot in UEFI before my most recent install (Ubuntu-mate 16.04).

CSM enabled in my ASUS UEFI-BIOS means UEFI+Legacy Oprom are supported, which I assume means attempt UEFI first and fall back to BIOS Legacy if UEFI isn't supported.

Although I had to boot a couple times before my new Linux install was recognized by UEFI, didn't seem to have any other issues.
Just wondering if the 'disable Secure Boot' only applies to older versions of Ubuntu, or if there is some other advantage to doing so?

Ubuntu has been UEFI friendly for quite some time. The short answer, IMO, is to leave Secure Boot on if you can. If Ubuntu (or any distro) will not install with Secure Boot enabled, then disable it and/or try other UEFI settings to make it work. Sometimes disabling Secure Boot will also toggle CSM/Legacy to enabled. There is a lot of variation in the UEFI settings between different manufacturers, so I don't think there is a one-size-fits-all answer to these problems.

ok thanks, appreciated!