Broker Data, page-102

Well you can see who is buying and selling. It helps paint a picture.
If there was a sharp price movement, you can see who caused it.
You can see who is accumulating shares. Who's dumping etc

For example lets say a bank that participated in a credit raise at 10c decides to sell and take profits every time the price hits 20c. This would obviously hold the price back, but once they finish selling you can anticipate the price will start to move again. You can see this in broker data.

Another example would be if retail holders are selling but all the instos are buying. Since they have more knowledge and resources than most regular folks, you might want to question what's going on. Or vice versa.

It's up to you what you take away from it.