I might need four different (distinct) roles filled but only have budget for three employees. I’d be prone to advertise (and genuinely recruit) all four roles, and hire the first three that I find a good fit for, delaying the fourth until/if additional budget frees up.

I might be willing to hire for two different levels of seniority/experience, but only one xor the other, not both.

Or be willing to hire for a role in Boston, London, or Zurich, but only one of those.