Would you buy a house without a fence or a wall? I don't think you would. It's not safe AND your property is open to everyone and everything.
Now, imagine that house is you. If you don't set healthy boundaries, then you are like a house without a fence. Boundaries are necessary at work, at home, and with friends. And unfortunately the only person that can set them is you.
At work, if you don't have healthy boundaries, you will find yourself doing other people's work for them. You might even find that you are burdened with mundane tasks (that are not your job) because you allow it i.e. typing up those meeting minutes. Or you get to the end of a busy day but then you realize that you've actually done none of your actual work. It ends up frustrating you and makes you feel like you are not doing enough. It all comes down to saying no when it's appropriate, and doing it in a way that is respectful yet firm. On the flipside, you don't want to be so mean about it that you become known as someone that isn't a team player or someone who is unapproachable. That would be equivalent to a house that has walls so high that nothing goes in and nothing comes out.
Set your boundaries high enough that you protect yourself but still maintain a good working relationship with your colleagues and your managers. It's not always as easy as it sounds and if you do need help, you know where to find me.