Even if you work full-time at an agency or in-house you probably still get people inquiring about whether you do freelance work. Choosing to be a designer means not making a ton of money, so these side projects can be a nice way to get a little extra. But is it really worth it and where do you draw the line?
If you have been working as a creative for any length of time, and want to expand into other areas, feel you have learned all you can, or simply wish to earn more money, branching out may be an option for you. There are so many complementary skills designers can acquire to make themselves more marketable.
When I look at design portfolios, many of them are not designed to appeal to the client. If you are looking for a job at a agency that is one thing, but if you want client work, you better make a portfolio that appeals to clients. It isn't hard, it just takes a different approach and you need to step out of your designer shoes and into those of your potential clients.