Loading .profile from .bash_profile or not using bash_profile at all?

I am on a MAC running Yosemite.

Until recently, I only had a .profile, in which I added directories to my PATH.

Now I have a .bash_profile, which from what I experienced and later read online, causes the .profile to be ignored when opening a terminal window.

I read here that since .profile is ignored when .bash_profile is present, I could just add

. ~/.profile 

in my bash_profile to invoke .profile.

If this is the recommended way of doing things, why is .profile ignored by default when bash_profile is present?

Asked the other way around (similar but not identical question), what is wrong with not having a .bash_profile at all and setting instead all the environment variables I need access to from my terminal windows in .profile?