Inflation is great to keep the stock market afloat. That's about its only redeeming quality. The reason that most economists like inflation is the false premise that people will stop spending money if money starts increasing in value... but the vast majority of people are going to spend their money one way or another, cause they can't just stop buying food or paying for rent... and they're not going to skip out on what little fun they can have because it might be a little cheaper later.
Deflation is bad for the rich. Because it means their non-monetary assets are suddenly worth less.