Learning curve can be steep as there is no dedicated training program for new hires. You might be expected to read up on things in your spare time. Could be challenging for people who prefer a more formal and structured job training program.
Small workforce means that you have to have at least a cursory understanding of what your colleagues are doing, especially when people go on leave and you need to cover for them. Unsuitable for people who are uncomfortable with performing such ad-hoc duties.