I know a few founders that have had to let people go after aggressively hiring. They've ended up fine but when they first raised their seed round they went out and hired a load of people. I do also know a few that are incredibly slow at hiring and it's lead to slow product development and an odd balance in the team (They have more designers than developers). I think sometimes if you hire too slowly it's hard to add more people when you start to need them. Because you have such a tight knit team that can't really change how they work to allow a few other people into the mix.
Somewhere in between seems best, only hire folks that really understand and fit in your vision and hire people that are going to be key for where you are slightly ahead of now over the people you needed a month ago. The team I spoke about needed designers then but now that the team has more designers than developers there's an odd balance that has lead to a beautiful but not very functional product. Their homepage changes more than their product.