To let you pick what I assume is the lowest hanging fruit, what are the most significant short comings of e.g. Calc vs Excel? I use it casually, but "casually"

To let you pick what I assume is the lowest hanging fruit, what are the most significant short comings of e.g. Calc vs Excel? I use it casually, but "casually" in a way that would probably be at least equivalent to professional use in most cases, and can't recall ever ending up with a blocking issue. So I'm certainly oblivious to the shortcomings and would love to know!