In both NetCommunity and OLX you can add more than one query or lists when sending an email. Not being able to do this in NXT means you can't combine lists to send to multiple groups and every email needs to be specific which is way less efficient and forces you to create a lot more lists/
Also, more important, you don't have to undupe your mailing list; that is done by NXT
This is incredibly inefficient and a huge limitation.