Whether Bitcoin users routinely check emails on their mobile devices. The proportion would influence any design decisions for a given service.

As an example, if you were running a website that sells time sensitive products, perhaps one which expires within days for whatsoever reasons, it would be ideal to be able to notify your buyer as soon as possible. If the majority of your customers are not in the habit of checking their emails on the move, it may not be the ideal mode of notification. So you may have to explore other methods such as text messages, or perhaps investing in a mobile application that does the notification for your client although that may not be cost effective for most start-ups.