Most people will not charge their lipos above 1c, as it can damage the lipo or worse,

Lets say that if you have a
3800mah lipo to charge that @1c you would charge it at 3.8A
4000mah = 4.0A
5000mah = 5.0A

And so on,

The 50w charger you mentioned earlier will charge at a max of 5.0A,
Which will be fine for upto 1 lipo @ 5000mah,

it will not charge 2 5000 lipos any faster on a parallel Charging board as its maxxed out at 5A

To benefit from charging two 5000 lipo on a parallel charging board you would need 10A charge rate,

This gives 5.0A to each pack, this then allows charging 2 packs at the same time, saving time.