What do you mean by congestion? Just having a lot of trains?
If you think of congestion as just number of trains, then suburban stations handling local trains are very congested. They handle 100's of trains everyday, often trains running only minutes behind each other. An such stations can manage with just 2 platforms, because the type of train movement there doesn't need many platforms.
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Railways build platforms according to their estimates of how long trains will be detained at a station, and the number of 'route blockages' expected.
Rewari has 6 routes branching out. So, when they are building platforms, they have to account for the maximum possible traffic. What if they have to serve departures and arrivals simultaneously on 3 routes? Can they manage it with just 3-4 platforms?
What if they have to manage arrivals on 5 different routes within a short period?
And remember that some of these routes were single lines until recently, so trains would be held up for long periods at Rewari until the train coming in the opposite direction reaches the station. So, a train might end up having to be at the station for 30 minutes. In those 30 minutes, another train can come in on one of the single line routes, and that would have to wait for it's own crossing. All this while, there are freight trains and passenger trains moving on the other routes too.
So, for a 6 route junction, with single and double lines, you'd need a lot of platforms or else it would be a big mess.