[savanaly]

If nothing else, styling emails serves an economic purpose through facilitating signaling. The more a company expects that consumers will value it in the long run the more incentive it has to signal that fact, and a signal is only as good as it is expensive in appearance to the people being signaled to.

In this case, things like a marketing email or simply the follow-up email to signing up to some service provide that signal since the user can see how much effort was invested in making the communication look attractive.

[Spivak]

As a recipient of those emails -- not really. Clients block remote content by default and there's almost never a reason to load them, especially when they're used for tracking. Those 'pretty' emails will almost always look like a soup of image placeholders interspersed with text.