According to Adam D'Angelo (first CTO of Facebook, obviously a biased source) Facebook was able to implement features much faster than MySpace, which was a major competitive advantage for them. "I remember talking to an engineer who worked at MySpace who told me about how they had this huge list of regular expressions to try to prevent cross site scripting attacks, and whenever there was a new one they would make a new regex to try to fix it, rather than sanitizing html the right way."[0]
[0]: https://www.quora.com/Does-a-good-engineering-culture-matter...