Production can't easily saved in grain silos, so money must be used to buy it, or it should be lent to someone that will use that production productively. If no one needs to buy hard drives ATM, then the hard drive company goes under and there is no better next generation.
Money is a means of allocating production. If it is just stored under a mattress, it isn't being useful and production is being wasted. We capture the negative effects of that waste with inflation.
Deflationn is basically a death spiral for an economy, as everyone consumes only essentials because everything will be cheaper tomorrow; lots of production is wasted because it can't be saved easily for tomorrow, people are laid off, companies go out of business, it sucks. Wars have even been started over silver and gold's deflationary tendencies (e.g. See the opium wars).
Don't confuse inflation with hyperinflation, the latter of which just destroys trust in the currency and makes it useless to save at all, causing runs on all production and starving investment. A bit of inflation is all that is needed to put money's use into a positive state without flipping in the other direction.