I typically recommend dudes do a stock flash only if they're experiencing strange issues with the phone...like it randomly freezes up and when you go to soft reset it, it hard resets the phone. VERY annoying. So I flashed to a Stock ROM, hard reset, flashed custom, hard reset...never happened again.

I should note, I flashed to another ROM thinking it was ROM specific and the issue followed me until I did the "stock flash dance".

So yea, I don't think it's necessary to go stock before every flash, but some dudes def do it as a matter of personal process.

...be a risk taker dude, just flash!

Hope that helps some.