The following post its based on my current experience working with some IT companies (names which I will keep as anonymus to protect their identity). And remember any resemblance to reality is purely coincidental.

But that are just 2 lines of code right?

As a developer generate code is our daly task(well among other things), and for us it seems not very important the work that we do on our daly basis, but each line of code represent a small step to solve a problem, in many cases solve that problem will release some company stress. In fact anything that you do, generate more money that you can perceive even if you are doing work as a freelancer. Lets say that you are found some bottle neck over the project that you are working on, it maybe took you 15 minutes of your time to solve it, did you ever ask you what represent that small fix? maybe that fix it will increase the traffic on the site which is translated to more views to a new product to sell. In other words your small fix is bigger than you think even when your boss said: "but that are just 2 lines of code right? that will be easy". From developer to developer: I will say you: Your Work is Worthy

You own the code, until...

Lets say you are a writer and you wrote a master piece, what would you do? The logical path says: go and register like an intelectual property. But you are just a software engineer and you were formed with an Open Source culture(which is good) but you are working for companies that have customers who want some confidentiality and the tecnologies that you use have an open source licence(except on entreprise tecnologies), so where are you?
Well basicly all the things that you do as a product of an intelectual process it is yours, but when you sign a contract you enter in a legal agreement that gives all your rights over the code to the company in some cases those contracts never mention the intelectual or industrial property which is completely wrong and from my point of view is irresponsable. In the case of the Non-Disclosure Agreement (NDA) that will allow keep safe all the industrial secrets that you might encounter inside the corporation. This document can be used to restrict you to leak any kind of information, including design and code, but that doesn't gives them the rights over your work, only restrict you to said something.

What the company owns

There is a gap between Intelectual property & Industrial property, and the software is one of those thinks that balance between legal terms. As an individual you possess every thing that you build and it depends on you on how you will distribute( the license is important ) in that case the product it could be consider as a intelectual product. But when you sold your soul to a company, the things change a lot, because everything that you work with is an Industrial Property and it belongs to the customer or your company, it depends on the legal agreements made it above you.

The hidden risk

The lack of this legal points on the contracts, left naked the companies and without any kind of legal protection, and it will leads to some open doors to corporate espionage. Let say that your competency hires a developer to be spy your company with the mask of a harmless employee, that is not the door you want to be unsecured.
In the other hand the abuse of legal restrictions, will kill the creation and consume of content outside the company, excluding the company from the rest of the world is not a thing that you want as a publicity.

The good guy ethic

The ethic lead us to be a nice guy even when the company where you work for, explodes you or wont gives you the law benefits. The motto of google is well known as "Don't be evil" and it works, but also you are the owner of your ideas, so at the end of the day if your current contract avoid those points, legally you can do whatever you want, but I recommend you don't do it.

Just be cool, and just share what you learn