It is often said that the molecule simulation for drug discovery will be one of the most important applications of Quantum Computing (QC).
As we all know that the entire process of new drug discovery is a long and costly process.
How critical is the molecule simulation in the entire process of new drug discovery?
"Is molecule simulation by quantum computing critical for drug discovery?"
No. Drug discovery is happening right now, without quantum computers large enough to do anything that a classical computer couldn't do decades ago. So quantum computing is not "critical" for it.
Currently, polynomial scaling methods like DFT are used to study candidates for pharmaceuticals, and some people even think that those calculations are overkill, though quantum chemists and quantum computing researchers (who try to make a living off of selling the importance of their research work) would say its underkill. The bottom line is that drug discovery was happening before DFT simulations became popular, and it's still happening now (without quantum computers).
So how would quantum computers help? For molecules in which the accuracy of classical algorithms like DFT, CCSD(T), etc., is not good enough, the hope is that quantum computers will be able to do more accurate calculations (for example at FCI level) with less cost than classical computers would need for such accurate calculations, but currently it's hard to imagine that happening any time soon because the sheer cost in terms of the number of logical qubits and auxiliary qubits for error correction seems beyond what we'll have in the next decade.
Keep in mind that we can currently do calculations with FCI-level accuracy in the important digits, for systems with dozens of electrons, on classical computers, but that level of accuracy is not seen as important enough so people instead simply use DFT and maybe CCSD(T), but it's just not seen as worth it to do FCI-level calculations for drug design. If quantum computers could do calculations with FCI-level accuracy for the price of DFT, then surely we would use them, but with DFT costing only $\mathcal{O}(N^3)$ for $N$ electrons, it's hard to imagine quantum computers becoming relevant in the 2020-2030 decade, unless there's a huge breakthrough in the technology (I think breakthroughs at the algorithm level won't be good enough).
