In the last few years, and since the financial crash in 2008, there have been significantly more start up companies. More people are becoming self employed, which have in turn led to the formation of small companies. If you are thinking of working for a start up, below are some pros and cons to help you with your decision.

Advantages of Working in a Start Up

As there are fewer people in the company, you have a bigger chance of being more visible to the people who make key decisions. This can mean promotions are more easily achievable.
You'll be working in a fast paced environment as decisions are implemented faster as rigid structures aren't yet in place
Your actions and outputs are more visible and this can be very rewarding
Business processes and internal politics are more visible. You get to see how departments interact with each other and compete for limited resources.
If you just need an internship and are willing to work for free, then it can be more easy to work for a start up. From my experience, start ups are very eager to get free labour.

Disadvantages of working in a start up

Pay and job security is going to be significantly lower.
Flash offices, flash IT systems may not be set up, lots of things may be very manual. Developed companies have already automated tedious tasks, so you could be spending more time working on more analytical and challenging projects if you worked for a more established company.
Your professional growth may become tied to the rate of growth of the company. If the company begins to slow down in its progression you may find that it is not enough to keep you stretching your skills and development.

My personal experience having trained as an accountant at large accountancy firm is that if you have just graduated from university/school, it is better to work for a larger established company where you can see how things ought to happen. Then when you have that experience you can implement those things you learnt into a start up, where work can be much more rewarding as your outputs have more impact. However for other specialisations working in a start up may be the right one for you.