Huh....as a trial lawyer who conducts discovery and loves reading juicy emails in discovery...I don't entirely agree. I put "important" things in email all the time, and have clients that do so as well. BUT, I'm referring mostly to ministerial important things, not strategic things.
"Remember, we have to get that order of 100 widgets to Spacely Sprockets by 5:00 p.m. on Thursday. Have we got shipping lined up?"
vs.
"Remember to get shipping lined up for the 100 widgets that go to Spacely Sprockets. Gotta get there on time, because you know what a whiny dick that Spacely is. And I sure hope he doesn't inspect them too closely, because we've been cranking out at least 5% defective widgets in each batch this week."
Important stuff can go in an email. SOME important stuff definitely should not. And yes, phone calls are so much better for all of those sorts of things. I much prefer the "Hey, there's something I need to catch you up on, time for a call?" message than "We need to talk about Bateshorn. He keeps walking down the hall with his dick out of his pants, and I think he might be drunk today, and also, I like the new secretary hire. Great tits." MAYBE don't put that stuff in writing, fellas.
CYA emails -- a real thing. Damn right. Few things are more gratifying than a client starting in with "you never told me..." and you quickly pull up an email that says "the fuck I didn't -- I told you the whole thing, including the expected consequences, on September 3rd. After our 30 minute phone call discussing that very thing, as referenced in the email." For me, it wasn't with a client, exactly -- it was a third party arguing that I hadn't properly informed my client about something that they then acted on (they never should have been granted access to that information, but the bankruptcy court said "fuck your privilege.") Fine. Here's the email, on-point, and in advance of any action taken. Suck it, fucker.