A possible problem with a multiwire circuit might be: If one side of the multiwire with shared neutral has a large transient load (like an air conditioner or fridge turning on, or heavy loading of computers and other such electronics on it(big spikes of current at every peak of the powerline voltage), the neutral and the hot that is serving the big loads will have voltage drop, half of which will appear on the neutral. But that voltage drop on the neutral will look like a voltage *increase* on the othr side of the multiwire circuit, and if severe enough it could blow up loads on it. Separate neutrals won't have this happen. But the neutral gets shared at the panel, but that neutral us usually much heavier and have miminal voltage drops.
