For example, say that you met somebody who is already working somewhere, and through the course of networking you understand that they're not happy where they currently are but they're not actively looking for new work either. If you decide that you'd like to poach them, then you must necessarily take a slower approach, since they're not being actively pursued by other companies (since nobody knows that they're on the market) and you want to make sure that they'll be happy at your company and everything else that's an essential part of recruiting.
On the other hand, take a senior engineer who left their last startup because the startup went out of business, and whose skills will be in high demand by many competitors. You have less latitude as to how much time you can take during your hiring process before they get hired out from under you by a competitor. Committing to never hiring quickly is a recipe for filling your ranks with mediocre talent.
Google, for example, was apparently very good at hiring (slowly) - at least in their early days. So it didn't matter that they were (are?) terrible at firing.
Facebook was the opposite AFAIK. It didn't matter that they hired too soon and too many of the 'wrong' people - because they were good at letting them go before it did too much damage to the business.
On balance, I'd rather be good at hiring than firing, as it seems to be much more fair on employees.