I would add that you need to consider recoverability. When the data and log files are on the same drive, you lose the possibility of being able to do a final backup of the tlog before a restore if the drives with the data files on it crash, because the log files are on the same crashed drives. So as long as a "point of failure" restore isn't required, then it could be acceptable for the data and log files to share the same drives.

If I lived on an island that only had pigs, I could have bacon.

If I lived on an island that only had chickens, I could have eggs.

But If I visited both Islands from time to time, I could have bacon and eggs. Mmmm. The whole is greater than the sum of the parts.

I am a better administrator because I am a developer. I am a better developer because I am an administrator. IT, and our world for that matter, is a system of systems.

Go! visit the islands! And enjoy the bacon!