For big fish, you're elastic will bottom out quicker then you have to hang on and hope the line breaks and not your pole. You should get smaller fish in quicker but the elastic being tighter means you may bump some off. In the end it's not worth it unless fishing the far bank of a canal (or similar) where you have to drag the fish away from the snags before the elastic stretches too much.
If fishing n0.3,4,5 elastics for small fish it is sometimes useful to have the elastic just through the the telescopic top section of your match kit.
The reason is so that if you are fishing a canal type venue in shallow water you can quickly steer the fish out of the swim to avoid spooking the shoal.
i elasticated my match kits last year just through the top telescopic 2, and when using lighter elastics on the canal it gives greater control when fishing the far bank. from now on i wouldn't go back.