無駄にする (waste)

The set phrase 無駄にする, literally 'make X into waste,' meaning 'to waste X' or 'to squander X.' Takes a noun (time, money, effort) as its object — 時間を無駄にする ('waste time'), お金を無駄にする ('waste money'). The negation ~を無駄にしない expresses the value of using something well rather than letting it go to waste.