The immediacy of blogging means you can satisfy your desire for self expression very easily. If you're passionate and creative this is reason enough to throw yourself into it.
Liberating and exciting
You don't have to be making any money from it. You don't even have to have many readers. Just getting your thoughts out onto the web for others to read is immensely liberating and exciting. Best of all, you can do it in your own way without having anyone demand any changes.
But the obvious freedom this medium affords contains within it a kind of trap: The longer you write whatever you want, whenever you want, the less able you are to take criticism. You can even become inflexible when it comes to writing style.
Becoming selfish is a risk
This can have an effect on your earning potential if you do make money from freelance writing. Being so used to doing things entirely on your own terms, you can become not only less adept, but also less motivated to write in the way that your prospective clients require.
Even if you don't write for money, it can be deleterious to the blog itself. This is because you can end up blogging for yourself entirely, and eventually end up figuratively disappearing into your own mind! You can alienate many readers this way and ultimately lose them.
Your readers should come first
The way to counter this tendency is to constantly remind yourself to keep your readers in mind. Before posting, ask yourself: Am I only doing this for myself, or is there value for readers? Would they enjoy this content and want to share it?
Do this and you'll retain the buzz of writing on your own terms, while still offering value to readers and thereby growing your audience. And if you write for money you'll remain open to outside opportunities and flexible enough to complete them in an accomplished manner.