Fundamentally, actions tend to be ends in themselves or instrumental ends to some other purpose.
Therapy seems to be one of those things that people think of as ends in themselves, but should be instrumental to other purposes.
The generic reasoning for why indefinite therapy is good is a combination of support being good, and self-awareness being good. Yet, without some understanding of what you’re trying to achieve, endless therapy may be counterproductive to better mental health.
Let’s say you’re trying to get over your agoraphobia. Insofar as you’re unable to be outside, or you’re failing to make progress to do so, your therapy is failing you. Even if therapy makes you feel good, the ultimate goal is for you to be self-sufficient and able to self-regulate going forward.
If you come to rely on therapeutic support, I think a disservice is done to you. First, you’re on the hook for the money that the therapy costs. Second, this dependence may put you at risk when you’re unable to see your therapist.
If you are always feeling comfortable within your therapy sessions, and you don’t hear ideas that reflect doubts upon your interpretations of the world around you, you may not be getting what you’re paying for. In order for patterns to break, change needs to happen. Change tends to require some discomfort.