I can only talk about cubase, but what your describing is just alternate ways to do things - each to his/her own.
Things like Halion, for example - 16 slots to match the maximum 16 MIDI channels. You can open one instance of Halion, and then create 16 MIDI tracks and in the inspectors end the sax to the sax MIDI channel in Halion, the piano to the piano channel. I don't do this. In Kontakt, you can create multiple instruments each on a different MIDI channel.
I don't do it. If I want a sax sound, I'll pick the right VST instrument and it becomes the track. No MIDI channel, just the instrument channel. I can then treat it exactly the same as an audio track, and use sends, reverbs, eq and pan it exactly as if it was an audio track. If this means ten instances of Kontakt, and a few Halions running to, plus all he rest - all is good, and I can get to things quickly. If I have MIDI tracks, then I have to remember that that just controls another track, and it slows me down, so I don't create MIDI channels at all - just instruments. Sometimes I might even have umpteen versions of the drum VSTi - one for each individual sound. It works fine this way for me, and I've been doing it this way for years now.