I used my wife’s $50k allocation once because I was held up by some paper work (you need a lot of paper work, notarized, etc…). They didn’t ask any questions about what it would be used for, but this was 2016, and they changed the rules a few months later.
Also, things have changed _considerably_ since 2016 (as these things tend to do). Indeed, nobody --- foreign or domestic --- needed to document use as long as you stayed within the $50k (you would be asked to if you went above that). Later it became a mandatory question, but wasn't enforced. These days it is enforced rather strictly. If you claim education, you need to provide statements of tuition and housing etc. For tourism there's similar requirements, and usually they limit discretionary spending budgets to ~$10k.