The largest company I've ever worked for had about 100 employees; not really a large company compared to most. The company did software development for a large vertical market insurance claims processing application. My job was the development and maintenance of an internal-use only CRM/trouble-ticketing application (it had other functions as well). I spent 8 years doing that, then one morning I was "laid-off" out of the blue. I was told my position wasn't needed anymore, and that they were going to look for replacement software for the app I developed. They gave me a month's severance and showed me the door. I later learned they were selling the company (to Tata), and I was basically "dead weight", in that my product was an internal-use only application, and not sold outside the company, and therefore I looked bad on the bottom line.
A week after I left that company, I had another job (with a very small company - 5 employees) developing a web-application and making 10K more than I was at the other place!
Four years later I went back (had to pick up a package that got sent there by accident) - I found out they were still using the application I had developed; they had not been able to find a replacement app that could fulfill the same business needs - unfortunately, they didn't have anybody who could update the code or fix bugs, but the fact that they were still using it says something (good or bad, I am not sure). That was two years ago; I imagine they are still using the application (I wonder if its been upgraded yet?).
I just wanted to tell that story - the moral is, no matter where you're at, large or small company, and no matter how long you have worked there - they really don't give a crap about you. They'll sell you out as fast as punch, if it means a few more dollars down the line. Besides that little tidbit, the other thing to keep in mind that you don't see as much in a smaller company (because everybody typically knows what everybody else is doing) - is politics. I am now pretty certain that politics played some role in my being laid off; what that role was (beyond the economics of the situation), I am not sure, nor do I really care. I know now that I can't last very long in such an environment, because I don't play that game - I really can't play that game. It involves something that I have never been good at, and will never be good at: Socialization. If you are typical of the majority of humans, though, then you probably socialize fairly well - so you might want to play the political game, and keep an eye out on certain things (I can't be less vague - because I don't pick up on various social cues and such - I really don't know what is going on or how to describe it; it probably makes me an "easy mark" for these kinds of situations, unless I am made aware of the issue in some manner beforehand).
Lastly - practice CYA - "cover-yer-a**"; log every bit of time you work and what you worked on, each day, into a log-book (use an engineering logbook or the like, where pages can't be ripped out without knowing):
Eureka Lab Book, Inc.
This will help you to keep track of projects, and it will also allow you to review notes and ideas from the past, for inspiration and guidance on projects. If you keep good notes about everything, someone later can't come back and tell your boss you were supposed to do something when you didn't know about it, or that you did something you shouldn't have (when you didn't), or when a colleague attempts to claim an idea of yours for his own.
Good luck at your new job!