Having coin tied up in LN channels removes flexibility when compared to using on-chain transactions to whoever you are trading with. This is because you are restricted to spending amounts the network can support based on available routes. This will always be the case, but the issue is pronounced today because LN is still in its infancy.
You can still pay someone on-chain with the coins you locked up. Right now, you can use third-party services like
Boltz,
ZigZag and
Lightning Conductor. However, this solution is prone to routing failures, which are less frequent now thanks to
multi-path payments (MPPs).
Using a third-party service to make an on-chain payment/transaction requires some amount of trust, and these services will typically charge some amount of fee.
MPPs should reduce routing failures, which should lead to more people using LN, which should lead to higher overall capacity.