> Reserve, even when you think you do not need to. A few euros for a Sitzplatzreservierung is the cheapest insurance in this entire system. On a delay-day, your reservation is the difference between a four-hour journey at a table with power and a four-hour journey standing in a vestibule next to the toilet.

Except when it is really crowded, reservations are revoked.

On delay-day you won't be travelling on the train you booked. So the reservation will only help if things go reasonably well. Which depending on your itenary might be less frequently than desired. Yes, a reservation helps if you happen to be on the correct train, but many others are not. It all remains a big gamble, you never know...