Use ～ないうちに when you want to act while a change has not yet occurred — typically to seize a window of opportunity or to head off something undesirable. Unlike neutral ～前に, it carries the nuance "before it's too late / while the situation still holds," so the main clause is usually volitional (～しましょう、～しておきます、～したい) or an instruction. Very common in reporting and negotiation contexts, and slightly more formal in writing than 「～する前に」.