Is there any advantage to damming a river?

Answer 1

There are several advantages of damming
1> helps provide irrigation
2> stores water for water deficit months
3> Hydel electricity which is the cleanest form of electricity can be generated.
But there are some disadvantages too
1> causes water-logging
2> sometimes leads to earthquakes
3> areas downstream do not get water. Its flora, fauna, marine life is affected. Many species belonging solely to that region become extinct.
4> Dams sometimes make flood management difficult. In many cases they actually aggravate the flooding when their gates are suddenly opened.

Answer 2

Several.
Damming can regulate the flow over the course of a year, preventing floods.
Water that accumulate in a reservoir behind a dam can be used to produce electricity.
Of course, damming a river also has some disadvantage. But you did not ask about them, did you?

Answer 3

Yes, if you are a beaver.