Note that doing that in Ireland for intercity will result in you being _severely_ overcharged. Dublin to Cork is like 20 euro if you book in advance; I think if you buy the ticket in the station it’s over 60!
It’s fine for commuter stuff, of course, but I assume that’s the case everywhere.
We are discussing having an Interrail pass. Are you talking about purchasing tickets without a pass?
The pass covers intercity trains and reservations are optional
Then you get situations like a last minute (ie: knew 30 days in advance) trip from Munich to Berlin where we found it cheaper to rent and fuel a car for two.
Sure we had to actually do the driving, but hard to turn down a journey on the autobahn as a tourist.