We love having access to our entire list in one place! It's so easy to see what campaigns are working well or not as far reaching outreach goes (i'm sure this can be done manually too but it just makes sense if we have an email contact list).
I wish there was some way of exporting data into PowerBI/Tableau - maybe someday? Also would like ability import from Google Sheets which could then export back out again using formulas etc.. Have been able create custom segments within my lists without needing additional software packages such as Mailchimp.