For Some businesses, email lists don’t account for much, but that is not the case for all businesses.  For example: Your Email list can be used in Facebook/Google/Bing networks for
Remarketing efforts.  Furthermore, the data accrued on the people on your email lists can create similar audiences, prospects for your goods/services offered.

As for the Email list itself, for many clients it cost them more NOT to have an email list, than to
Accumulate and manage that direct response list.  The Fact is, you already have a rapport with the people on your list, why not expand upon that.

Example:  Foreclosure attorney worked for had emails scattered, when the economy began to recover many of his clients were in a position to rebuild their credit.  So When he came to me asking how much more should be allocate towards the budget to increase client base towards credit restoration, it was much to his surprise when I told him “Nothing – Zero – We use the email list of clients past and we utilize direct target marketing with previous clients”

Now of course, he was not very organized when it came to keeping track of the emails, but we compiled the list, and kept tidy records from that day forth.

The point being, it would have costed him more NOT to use the email lists, than to use it.