This risk can be great, but the team and company can be organized such that the risk is extremely reduced. A pairing schedule, for example, can be very effective.
1) This person is talking directly to clients day one, solo
2) Their code is pushed without review...
3) They are making high-level (C-level, maybe a bit lower) decisions for your business
Otherwise, yeah... a bad employee can do some harm. But, it's that employee's fault, and the other employees will realize this.
It is the business's fault if they go a year under-staffed because "they are afraid."
The second is MUCH more damaging: shows your leadership is not bold, they are misguided, and they don't know what to do to correct course if something goes unplanned (sub-performing employee).