In order for parachain to communicate with each other, they need to have a HRMP channel opened first. Currently the maximum number of HRMP channel allowed on Polkadot 10.
We have 21 parachains at moment and Acala and Statemine both are already have 5 channels and working with many more parachains on opening more channels. 10 channels is simply not enough.
Kusama have already raised the limit to 30 with this referendum and currently Karura is having 19 channels and we have no noticeable performance issue due by HRMP channels.
This proposal aims to increase the maximum number of HRMP channels from 10 to 30.
30 channels should be enough for at least next few months. We have another proposal to increase further if any parachains are approaching this limit.