But you can still use the main chain if you prefer. The most useful would be for example if institution A does a lot of business with institution B, instead of spamming the main chain with thousands and thousands of operations, they can use a channel between them (less fees, no delays, privacy).
Agree, big institutions that trust each other will benefit from lightning and this may boost XML to the highest hight. Also this should lighten the main chain that could give people an edge..