Actually I use the Virus TI (Polar) with the master effects switch turned off.
To me it’s mainly two things: the interface is one of the more immediate sort, and it is 16 part multi-timbral, which fits nicely my way of working.
Compared to my NordLead 1 I find the sound somewhat more direct and snappy. But I have to admit that I have never engaged them in a 1-1 comparison. It is just pure perception.
Bottom line – why do I have it? I guess it’s the chemistry.