They are not mandatory, but they can be sort of a "safety net" so that it's more difficult to dial very harsh tones. The single most important thing really is to keep it real: don't do 5 different eq's and two drive pedals and three amps with all the advanced parameters tweaked. Take the amp at default settings, flip through the IRs and when you find what you like, you are 95% there. This kind of sounds are realistic and will work in wide variety of situations. If at that point it sounds bad, chances are that something is wrong: basic settings, bad monitoring speakers, bad whatever, I don't know.
I've lost count how many incredibly complicated and stupid patches I've downloaded from AxeChange and this forum, with four rows of incomprehensible mess and random routing, that in real life would look like this:
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