I have concluded that, for Fedora 28 at least, it is better to leave a system in UEFI/Secure Boot mode if your goal is to install a multiple-boot system with a boot menu offering a choice between Windows and Linux.
How I discovered that you need UEFI for multiple-boot with Fedora 28
I am not a fan of UEFI/Secure Boot, but have found that modern hardware has fewer installation issues with Windows and Linux in UEFI mode. So in the past 12 months I have been leaving the BIOS in UEFI/Secure Boot mode.
When I reformatted a system in Legacy BIOS mode, first installing Windows while leaving some unallocated space on the hard drive, then installing Fedora 28 Linux, the grub boot menu did not include a boot menu entry for Windows. Attempts to create a manual grub menu entry for Windows did not result in a successful boot.
How to create a multiple-boot system
Until recently, I installed Linux by first reducing the size the Windows partition, creating unallocated space, then by installing Linux with automatic partitioning enabled. In each case, the Fedora 28 installer used the unallocated space for Linux partitions, and created a multiple-boot menu with Windows as an option. What I did not realize was that the Fedora 28 installer only does this operation correctly if the BIOS is set for UEFI/Secure Boot.
Why use a multiple-boot setup?
Linux on the desktop offers functionality, performance, and security benefits over Windows. However, there are certain edge cases that require Windows. Rather than simply giving up and letting Windows win because of one occasional “must-have” application, I configure some of my machines as dual-boot between Windows and Linux.