Is inflation always bad for economy?

Inflation is certainly not always bad for economy, in fact a moderate level of inflation matching to it's growth rate is good for the country. Moderate inflation suggest demand in the system while no inflation or deflation suggest demand collapse which is much more dangerous than Inflation.

For Instance US inflation is 1.5 to 2% while it's growth is 2-3%. This equation is ok. A Country having an inflation equal to it's growth rate is not bad though it is always preffered to have lower inflation and high growth rate. But it is difficult to achieve on a continuous basis.

Reserve banks all over the world prefer and try hard to have moderate inflation and would worry if there is a situation of deflation. But too high inflation will make the currency of the country very weak against the major global currencies and will bring the economy to it's knees, like what happened in case of Zimbabwe.