I've found that "send me a spreadsheet and I'll upload it" isn't a great user experience. It's just a big pile of cells, with no documentation (which they wouldn't read anyway).There are a billion things they can do wrong, and they get no feedback on it until I email it to them. They don't know what the options are for any field, and it's easy to enter a nonstandard value. A typo in a header row can lead to data loss with no errors.

There are times when it's the easiest way to handle things, especially for experienced users. But I find it a massive hassle to maintain support for every possible mistake the user can make.