An instance of Kontakt is 38Mb..that is ~0.5% of RAM on my small system.. so whereas YES to be pedantic technically it is a waste of resources, but practically its not the player than uses resources, its the instrument and the use of it that consumes resources.
Irregardless, at the end of the day, more ways to configure and see your tracks is better,
as long as we dont start walking down the path of losing abilities we currently have.
However the discussions above have nothing to do with the OP request, which was a potential Sonar user wishing to arbitarily change the number of outputs from (say) Kontakt, after it has been instantiated because he a) does not know how many instruments he wants, and b) did not seem aware that he could simply hide tracks