Back in the day we used to talk about 'above-the-line' and 'below-the-line' as a proxy for advertising versus direct marketing (and never the twain shall meet).
Digital has changed all that - we need to redraw the line.
We spent ages arguing about whether online was direct marketing or advertising before we realised it could do both - as, today, can print, tv, radio and so on thanks to web addresses, call centres and text responses.
So let's not obsess about that line any more.
Let's think instead about the line between acquisition and retention.
I think this is a much more meaningful line, and the crossover point is the moment of 'conversion' - i.e. whatever you're paying your CPA network for (a sale, registration...)
Does this matter? Well, yes. I think it does.
Agencies in the UK (with only a few exceptions) are so focused on getting people across the line that they typically don't get engaged with what happens next.
Understandable, I guess, as that's where the big ad spends tend to be. And yet, for marketers who pay attention to this stuff, the other side of the line is where the real value comes in.
The other side of the line is where you continue the conversation your audience have invited you to have with them (they've given you permission to talk to them).
It's where you start driving relevance through dynamic content management on your website and using engagement marketing techniques like individualised RSS, email, mobile marketing or loyalty cards.
The penalty for staying acquisition side is a lifetime of playing the AdWords lottery every time you want to sell a widget.