When I was a child, I loved to travel by train, and more often (100% of the time), we traveled in sleeper class, which my parents could afford at that time. Later, after I grew up, with hectic office schedules and stuff, I tended to travel more by planes/buses (sleeper AC bus), and in case I happened to travel by train, I mostly tended to book a ticket in AC class.
Recently, to attend my friend’s marriage, I intentionally booked a ticket in sleeper class, as there was a huge price differential between sleeper class and AC class for a longer 15-hour journey in this case
Being from an MBA background, I tend to observe people and their behavior, and I have always tried to deduce logic for their behavior.
As I was traveling, the first major difference was how active the coach was compared to the AC coach, where it is always silent. Here, people are more animated and talk to other people.
The second thing is the vendors at the stations that we came across, who would sell their products at the window. So that you could experience different local cuisine and snacks. Whether you are buying it or not, at least you will know the stuff.
The third thing is that here, people are laser-sharp, and if you are not alert, people will take your seat (not entirely, but somewhat). They would occupy the charging points, even though there is no necessity for them to use the charger. Since they have faced scarcity every time, they want to use the facilities before anyone else, or else they will face the issue later. I think that mindset comes from the scarcity they face in their daily life.
Overall, if travel is an experience, one should travel in sleeper class, wherever you are taking the train for your journey.