I've seen several negative comments already on here, and instead of replying to each of them, I thought I'd just share my experience.
For some of us, this way of doing things "scratches itches".
I think I've always done this. If something interested me, I learned more about it, or I'd learn something because I had a need for it. Then I'd find out someone I knew needed something based on what I'd learned, and suddenly, I was making money doing it. In fact, this has helped me greatly in my life, because now I can be a stay at home dad and still work and do things I enjoy and that fulfill me. Currently, if you include being a dad, I have 4 "jobs". I'm about to add on a 5th on the advice of someone.
Each of these jobs is enjoyable for the most part in different ways. I still work a few hours for my old job, so I keep up those skills. I have a totally creative design job which I love because I get to be creative, and I usually end up teaching students as well. I have a coding job that allows me to use those logic and problem solving aspects of my brain. I have my horde of kids, which is fulfilling in numerous ways. And I have the new job, which is filling a niche not many realize or know about. It's small scale, but that works for me.
The key to all these things is prioritization and time management, and keeping your customers expectations reasonable. Yes, there are bad weeks when EVERYTHING hits at once and you have some really late nights. But this is a rarity if you are up front with your clients and explain the situation. A little honest communication goes a long way.
Now, admittedly, I'm not the best by any means at any of these jobs. But honestly, even if I spent every hour of every day at that job, I still wouldn't be the best. And I'm ok with that. I don't feel this desperate need to be the ultimate, because there will always be someone better than me. However, if I make the lives of others better, give a good service that they need for a good price, get to stretch myself while still managing my family, and get to learn new things constantly, where is the negative here?
I'm not saying this is for anyone. And to the person who feels that someone is being taken advantage of, seeing as you often choose how many jobs you have (people with more than 3 are usually by choice, not need, because those people would be working double jobs most often), so if you are being taken advantage of, it's only because you are taking advantage of yourself.
If you DO decide to do this:
A. Use a really good time tracking program (I use Time Recording for Android).
B. Know how to get your todo list organized (learn getting things done can be very helpful, and I use todoist to sync so wherever I have a revelation, I can dump it into my inbox).
C. Learn the value of honesty and integrity. Be straightforward with people. Honestly goes a long way, and if someone knows where they stand, often they will be more reasonable. And if you screw up, just admit it. Mistakes happen. Own it.
D. Know your worth. Know what is a reasonable amount to be making. Yes, we often make less than we think we are worth. But know what you are willing to accept.
E. Be reasonable with billing if you can. IE: you will likely work more hours than you get paid for (research, etc), either because you quoted a price and are held to it, or you know how much they are willing/able to pay, or whatever. But try baking that extra time into your price, or your expectation of self worth.
F. Accept you will not get along with every customer. Be really, really, really good to the ones you click with.
G. Word of mouth is still the best marketing for most small things. So, get good word of mouth.
H. Try to have a sense of humor and smile.
I. Know that life is short, and enjoy it. And don't expect work to be your self worth. That is where the danger lies. Use it to expand your world, but get your self worth from who you are, not what you do. And take breaks. I can take a month off if I schedule things right.
This will not apply to everyone. But please, don't say I'm being taken advantage of, or it's greed, or that I'm insecure. I'm not. I fill little needs in the world around me. I'm not desperate either. Please stop telling me what I am or what I'm feeling. I'm quite content. I'm not saying it will work for everyone. But it sure as heck works for me.