>>And as you said when we use a monophonic patch it takes less but the sound is cheeper
That's been pretty much the same since synths were ever built. The Minimoog has just 1 voice poly! The Jupiter 8 had, of course, 8 voices of poly. The Andromeda has 16. The Virus B has 24, the C has 32, and the TI has "up to 80".
etc.
Even though the TI is digital, it doesn't have limitless DSP.
But you really do have to take into account how you play a patch, and the type of patch you're playing, if you want to calculate how many voices it's using at any time.
A 3-unison patch playing a 3-fingered chord will use 9 voices of poly. Change chords, and it becomes 18 voices of polyphony while it still calculates the release phase of the previous chord. And if you're using a third oscillator in the patch, this can eat an extra 8 voices of poly, so you'd be looking at 17 and 26 voices respectively for the above example. It soon adds up, and that's just one patch.
The TI has a rough quota of "up to" 80 voices, but this is highly dependent too.
If you have lots of patches playing at the same time in the mix, you might not be able to notice if you decreased the unison of some of them, but it would give you a few notes of extra poly to play with elsewhere.
If you want to use several absolutely massive unison or very complex patches, then it's probably best to play them solo and record the track down as audio, allowing you to completely free up the Virus for other parts. Too many "massive" patches playing at the same time make everything sound muddy anyway, it's best to use them sparingly. What sounds big and fat in isolation may just sound muddy in the mix when mixed with lots of other big and fat patches. Those "cheaper" patches come into their own when mixing.
Try and work to get a fatter sound from fewer oscillators (by programming, using the modulation matrix, using midi CCs, etc.), than throwing more and more oscillators into the fire. The Minimoog had just 1 voice, but that one voice certainly wasn't cheap.
