I can't speak from my own experience but I can speak for a parent who worked in this field their entire life.
This job depending on the person/family/case can impact you in many various ways for the good and the bad similar to any job but with more emotion tied to it because you are dealing with humans.
On the good side you get to positively impact people and steer people and families down paths to lead them to success which you get to see and feel. This work is challenging and wins lead to great successes and mental rewards for you are the person leading the conversation.
On the bad side there is a lot of human emotion tied to it. You have to really be able to divide work from your personal life and not create mental piles of memories that are of a negative or bad experience with someone or maybe you are worried about someone in your personal time.
I would say the good out weighs the bad as making a human impact is possibly the most rewarding thing you can do in this world.
I see myself more as counseler than therapist . For ease of understanding let's say therapy is more intensive long term engagement.
Now moving forward to the question.
Being therapist/counselling can be both fun and challenging.
It can demanding when you are not in mental state of listening someone.
It is hard when you sometimes got to study more after session to understand clients situation.
But it is fun when you see clients improve.
Client not always get better in magical way but when compliance is present they surely make difference in there life .
Oh and it is important to create professional boundary too I guess there is no better way to put it but "don't feel others problem as own" surely take responsibility for clients betterment but have awarness client have to do homework. It is there life. If therapist keeps feeling sad all the time because of clients life. It will effect therapist negatively.
That's why therapist often have safe space /healing way to release all those emotions of the day
The job can look very different depending on where you work. My current site is flexible, allows me to see clients and do my notes primarily rather than other kind of work in addition to it, and can be fairly unpredictable. Clients may show up, or no show, and note-taking systems and other systems can change fast! I would say it depends on where you work, but it can be very rewarding, flexible and fun, while also being a big responsibility, unpredictable and needing a lot of time for your own self-care! I think that is the biggest thing--making sure to keep onto your own mental health! That is your best tool and gift to your clients and those around you!