m18 R2, SSD questions, #2

Hi,  

I have the alienware m18 r2 4070 version.  I seen videos from dell where I could use a m.2 2280 instead of a 2230 ssd.  Does that mean I can now have two -  4tb drives?  It makes sense yet it doesn't make sense to add a m.2 2230 if the max capacity is only 1tb.  What would be the point of having a 2230 for?  Videos show users with using 2280 and 2230.  Why not just put 2280 in all slots?  2230 aren't any cheaper.  They're just dramless