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Given the following post, respond as if you're commenting on Reddit:
human
Why is 2% inflation generally targeted by central banks?

Why is it that central banks generally have a 2% inflation target instead of zero? I welcome technical explanations since I'm studying Economics at University and Macroeconomics is my favorite subject.
gpt
(Caveat: from a fellow undergrad.)
There are two zero-lower bounds that are the reason a small, positive amount of inflation is usually desired.

The first is the ZLB on nominal interest rates: the central bank cannot lower nominal interest rates in the economy below zero, because people would just hoard their money as currency under the bed, rather than lose it with negative interest rates in their bank accounts/investments.

 But sometimes (in some countries, right now!) negative interest rates are necessary to increase aggregate demand and restore output to a higher level. The real interest rate (the nominal interest rate corrected for inflation) is the one that truly effects people's decisions and is given by:

real interest rate = nominal interest rate - expected inflation

So with a small amount of positive inflation, real interest rates can go negative even though the nominal interest rate is bounded at zero. One thing the Fed in the US is trying to do right now is raise inflation expectations (partly through QE, and also through an announced "Evans Rule" which says they will not raise interest rates until either unemployment drops below 6.5% or inflation goes above 2.5%) so they can get a lower real interest rate.

The second ZLB is on nominal wage growth: empirically, we just don't tend to see workers accepting nominal wage cuts, nor bosses demanding them. Wages are "sticky". But sometimes a country needs lower wages in order to restore competitiveness in tough times, which is called internal devaluation. A small amount of inflation makes real wage cuts possible, even though nominal wages don't fall (real wage growth = nominal wage growth - inflation). 

Some economists (e.g. from memory Olivier Blanchard, chief economist of the IMF) have been suggesting that a slightly higher inflation target such as 4% may be better in the future, because the last few years have really shown how much of an issue these ZLBs can be. And a higher rate of inflation in normal times would help avoid the zero lower bounds. 

I agree that without these two ZLBs, zero inflation would make more sense. How nice it would be to not have the value of money constantly changing! We could easily compare statistics over time, people wouldn't be (incorrectly) convinced their living standards are being slowly eroded by this heinous inflation, etc.