it all depends what you do and why you do it.
For 95% of the population a normal +- 2000 calories a day meal will be more than enough. Considering you are eating enough from all the groups.
For athletes it's differents, good supplements can help you build more body mass faster, give you more endurance or as simple as give you more calories. There is so many supplements out there and so many opinions about them it can be very confusing.
When I'm weight training a lot, I like to take a meal replacement, gives me the extra energy, there are some important vitamins and proteins. I still need to eat my 3 meals a days with good food. If you spend 2000 Cal a day and you eat for 3500 cal .. there might be a problem in the long run.
Ernie