Csv is an ubiquitous data format. Especially when you're receiving data from external sources which you don't have control over, which often happens to be the case in banking and finance (streaming csv dumps are quite common)

CSV is stupid format. XML, JSON, YAML are better to read and easier to parse/validate. After compression these formats takes similar amount of space or even less when cross-referencing.

CSV, tab-delimited files and in general flat files are retarded idea to be used in banking. I know because I work for bank, these are source of all misery.

Adding to what bladecatcher said, even if you want to work internally with a binary format, the fact that you receive large csv datadumps from the outside means you'll have to transform them into your internal format of choice. The first part of that transformation would greatly benefit from a fast csv parser such as ParaText.

Another datapoint: data changes (price updates, number ranges) between European telecom operators are all csv files over ftp. You can recognize the security aware by their use of sftp!

"For example, if reading+parsing takes only 10% of the total processing time, then optimizing this stage will only give at most a 11% increase in performance."

10% performance increase is nothing to scoff at in a mature code base.