Boundaries can come in different shapes and forms.
Scenario - you have a impending deadline at work, and another team ask for your input on another project that they have a deadline on. The other project involves certain software that you you are struggling with on your own project and you are aware this can enhance the knowledge you need.
Do you say no as you have a deadline to meet?
Agree to give them a certain amount of your time, knowing that this will bring benefit to your own project and aware that you will have no issue letting them know when you have to stop to focus on your own project?
Agree to give them a certain amount of your time, but know that you will struggle when the time comes to say you have to stop?
Agree to work on their project sacrificing your own project and deadline?
1 & 2 would be healthy choices. It is for YOU to determine at that specific time what would bring you most benefit. Would you struggle to choose 1 & 2? Does this mirror in other aspects of your life?