A satisfied user here. Found it very useful when tools like cut and sort weren't enough, usually when I need to do a join on two different tables (err, files). Left joins work, but I don't think right joins are supported.
I've used this in combination with jq as well. I'll use jq to convert json to CSV, and then use SQL to do whatever else.
Same. You can go a long way with cut, sort, etc. and also awk with its pattern matching. But if you're handy with SQL, that can often feel more natural and certainly things like joins among separate CSV files, as well as sums and other aggregates, are easier.
If you have "unclean" CSV data, e.g. where the data contains delimiters and/or newlines in quoted fields, you might want to pipe it through csvquote.