Boundaries are invisible safety lines that every person needs to draw as it defines the range of behaviours that are acceptable for an individual in a given space. How far will you go and upto which point you will allow ingress into your space, is what boundaries announce. Boundaries are like walls. Don't hesitate to show the door to trespassers who do not respect the walls.
Your boundaries may hurt others. But that is their problem - not yours. If you cannot say 'NO' when people infringe your boundaries, you will hurt yourself. But if you do not set boundaries, it will reflect less of respect for yourself. And that will hurt much more.
Setting boundaries at work place is very important for both you as an an associate and for you also as a leader.
Power junky 'Bosses' at your work-place are corporate bullies. They first test the limits and if not called out, will form a habit of crossing the limits regularly. You need to be wise to gracefully indicate the boundary the first time itself when he/ she oversteps and infringes. Later, it may become too late. Your fear of losing your job may make you keep quiet. But that will make you lose your self-respect. A job, you can get another but your self-respect once lost, will corode you from within.
As a young General Manager, my wise ex-boss (late) Kersi Naoroji taught me a sharp life time lesson . He told me that a smart leader is one who knows when to put his arms around others BUT is wise enough to know when not to allow others to put their arms around his shoulders ! Thence I learnt the importance of boundaries !
Others see boundaries as limits. You see them as space for freedom with a prescribed frame-work !