Before Cakewalk implemented upsampling, I had to go through a very laborious process of saving out MIDI and audio files, saving presets in amps and synths, opening them in 96 k projects, rendering, etc. It was a pain. 
 
I don't upsample everything but there are some instruments and amp sims (as well as a dynamics processors sometimes) where it really makes a cumulative difference. When I render a final mix, if I don't have upsampling enabled, the overall sound quality is audibly and obviously less "defined."

Just Curious :
 
What happens if a VST or effect has Internal Oversampling e.g PRO-G and i turn that on (x4) then i enable the platinum oversampling (x2) also ?
 
is the result : ( 44100 project sample rate ) x4 Pro-G Oversampling ) =176400  x2 plat upsample =352800
 
or does plat not upsample plug ins that can oversample ?
 

As the old saying goes..."it depends." An oversampling algorithm has to operate in real time. Upsampling on render is an offline process that can take its time doing the sample rate conversion / rendering / "downshifting."
 
Upsampling can indeed make a difference with synths that oversample. Please check out the following video.
 

 

Perfect Video thanks