Thinking tool. Self-subjecting is a nice phenomenological tool for thinking.
Thinking about a concept that can be experienced, while you think of yourself experiencing it. It’s useful in thinking in the shoes of others, when buying furniture, setting personal goals, thinking about social situations or friends.
What it’s also handy for, is distinction between the other modes for thinking. It’s easy to conceptualise from yourself as the subject, but this is often not very practical since your ego can make things a bit messy without you noticing.