I can't stand excel. It thinks it knows what I mean and actually edits my data destructively, mistakenly, especially when I enter dates in day/month/year format. If you just import a CSV and then export it directly, it mangles the data. I will not tolerate such behavior.

If you have a column of phone numbers with leading zeroes, coming in from a csv, it decides it's a number and drops the leading zero, which breaks the phone number.