The trouble is, it has to mean something and be of use to the person receiving the email. I'm always astounded by how many companies think it's useful for me to know 'your stuff's on its way' without thinking I might be more than just a little curious when it's likely to arrive.
Adidas is a fine one for this. I've ordered several items recently and the brand always reminds me of one of those bores who knows a lot about a tedious subject but won't get to the point. Rather than just tell you in an email, they expect you to go to the main site, click on a link, then go back to the email and copy an order number, to then tell you a lot about where the order's been. There's eventually a rough estimate of when it might arrive but that's only after you've scanned through a very accurate, to the minute, tracking of when it came off a boat in the UK and was checked in to a warehouse. All of this might sound very clever. It isn't. It holds no value to the customer. Why not just tell the person what they want to know in the original email? "Your stuff's on its way and should be with you tomorrow." If that info is available after several clicks and cutting and pasting, why not just set up a system that tells the customer what they need to know in the first place?
Same thing with my favourite wine brand, Naked Wines. It recently confused me with a message saying my wine had arrived and hadn't arrived at the same time. Then, with the next order they said there was a problem with a delivery and I had to call. Turns out in the first case the order had been split and half had been shipped, half had not. I had no way of knowing this, of course. But the brand did, and there's nothing stopping them combining email with delivery data to say exactly that. The delivery's been split and half has arrived, the rest will be with you tomorrow. With the request to call in to clarify delivery details, it turns out the delivery had been missed, there really was no need for me to call in. Yet, there i was responding to a message some marketer thought was clever but was actually anything but. If the systems had talked to each other I could've just got an email saying delivery would be a day late, no need to wait on the line and listen to elevator music.
These are just a couple of examples but the list of dumb, automated emails people are fed up of receiving because they don't give them the full picture is endless. So go for automation, by all means, but not for the sake of it. If automation lets you combine data to truly help a customer, then get your tracks shoes on and go for it. If it's just going to send out a standard email that can actually hinder the shopping process or confuse customers, then think long and hard whether automatically triggered emails are necessarily the right thing for you. If you're saving a customer a need to call in, that's great. If you're making them search high and low as they cut and paste order numbers, that's far from great.