At this moment, it is only possible to include contact/lead related information to your Custom Event Trigger, used in a Customer Journey to trigger a Power Automate Flow.
It would be most usefull if your able to add a "open field" to the trigger, that can be filled in within your Journey.
expl 1) Creating a lead with PA flow, triggered by a Event Trigger Tile in the Journey
Now you have to create a new PA-Flow for every campaign, to be able to have e.g. a different topic per lead per campaign. If you could send a Topic along, you can re-use your trigger.
expl 2) Use PA flow to trigger external channel. e.g. sending direct mail, whats app, create phonecall.
You have to create a new PA flow for every campaign, to give context to the channel. If you could send a "template id" or something like that along with you Trigger, you can re-use one trigger for all campaigns where you use this for.
I can give tons of more examples, but you get the point, very useful!