Inflation is not a good thing because it slows down economic growth.
For example, when inflation is high, things cost more and people spend less. They also do less long-term planning that involves spending money, such as building houses and investing. Businesses are affected in the same ways. When inflation is high, it tends to fluctuate quite a bit. This uncertainty makes people wary of spending money for fear that inflation will increase even more and they won't be able to pay their bills.
High inflation also adds additional costs to long-term interest rates. These costs are to offset the risk associated with inflation. The additional costs make borrowing money less attractive. When people don't buy things (when demand is down), then the supply of goods gets too high, production has to decrease, and unemployment increases -- in other words, recession hits.
When prices are stable (when inflation is low), consumers make more purchases, investments, etc., production output is maintained and employment remains high.