I imagine that Slack's founder, who was formerly co-founder of Flickr, is experienced enough that he could avoid a lot of the pitfalls of raising too much money

I imagine that Slack's founder, who was formerly co-founder of Flickr, is experienced enough that he could avoid a lot of the pitfalls of raising too much money such as losing control of the board. Since this isn't to add runway, it doesn't make much sense unless he's not planning on selling to another company anytime soon. By my estimation, Slack is not too far from being profitable (or able to get that way), with ARR somewhere between $15M - $30M and only 125 employees. With this big war chest Slack could buy or build a few other collaboration tools. It'd be great to have a competitor to Google Apps at a similar price point.