Just noting comments by jforce and corkyg --
Only in the last two years -- starting 2014 -- did I feel it necessary to have a dual-boot system. And I chose to put both OSes in separate partitions of the single boot-disk.
It requires some minor attentions. For Windows Update, you want it to come back to the same OS selection if a restart is required, or you need to be present to manage it manually. Even for that, I don't think it's ever caused a problem.
It's also useful to have a utility for managing a dual-boot physical disk, like Macrium. Eventually, if you want to dump one of the OSes, that too is fairly straightforward. But again -- with something like Macrium -- you may want to resize the system-volume for the remaining OS.
But like Corkyg, I've thoughtfully installed my software on both OSes. It is probably a good idea to eliminate drive letters for one OS volume in the configuration of the second one, and vice versa. I also do not allow system protection volume shadow copies in one OS for the disk volumes of the other.
Haven't had any troubles with attention to those details. Macrium will image an entire dual-boot system disk, even allowing you to fold in other physical disks in the image. I guess the best thing to say is "you need to know what you're doing, and know what to do if or when something goes wrong." Otherwise -- works for me!