so far I've only worked at small companies. In my experience you get a lot of flexibility but you also have to wear a lot of hats.
Be knowledgable about design, development, SEO, marketing, handling clients. Constantly be on call for any emergencies, holiday cover can be an issue.
In the company I work for this is the first year in 7 years that I'll be on holiday and not feel like I have to constantly check my emails. (I was on my own until recently)
Whilst not all companies will be like this, if I were to leave I think I'd go to a medium sized company. More chances of being able to specialise.