Probably the worst thing that could be done with money is to spent it on war, or anything that causes destruction. Taxes can be used for highly beneficial things: highways, bridges, hydroelectric plants, medical research. Money in the private sector can be spent on destructive activities: casinos, bogus drugs that not only do not do what they are supposed to, but are harmful.
When money is spent, regardless of by whom, it can have a multiplier effect which is unrelated to whether the government or some private individual spends it.