The main problem I have seen is that data in Excel is essentially not validated.
Sometimes you get an number, sometimes you get a string containing a number. Sometimes the string contains white space that you don't want. And then there are dates, which can have similar problems multiplied ten times.
Sometimes you get an number, sometimes you get a string containing a number. Sometimes the string contains white space that you don't want. And then there are dates, which can have similar problems multiplied ten times.