With the eVic you can set it to "auto" so you only have to press the button once for a metered puff of as many seconds (to the tenth) as you want. Since it counts up time for every puff anyway, you can get a pretty good idea of what your average drag is and set the auto accordingly, and I suppose you could even determine how many hundredths (or whatever) of a ml each puff would be. I haven't tried to calculate that. Combining this with a record of how much liquid you go through in a day could probably help you to determine pretty precisely how much you use. I doubt too many people use this feature and I agree with DoogieTony, it really is more of a "toy" or useless feature unless you really dig record keeping and stats. Personally, I haven't found it to be very useful, but it is there if I want to play with it. Once you start trying to get that precise, it feels a little too pharmaceutical.
That being said, the eVic computer software is still pretty lacking and doesn't work right. The firmware on the device is pretty cool though. Sometimes it is fun to look at the puff counter to see just how many you go through in a day though (IBCR Media: it counts how many times you push the button, not how many times you take a drag while it is pushed. That could be where the auto feature is useful to some though). I have found that a heavy day for me is in the neighborhood of 300 puffs. Average is more like 200. Like Wbart said, it all kind of depends on your nic level too. If I was still at 24mg, I imagine my puff count would drop quite a bit. I stay at 18 which works nicely for me and the frequency at which I use my device. On days where I find myself chain vaping, I will sometimes even change to an atty with some 0 nic samples I have received and go nic free for a period of an hour or more at a stretch. I have noticed no ill effects from this and if I feel like I need the nic, I'll switch atties back to one with 18mg.