I’ll be taking the train from Lund, Sweden to Aarhus in early September. As I browse the website for schedules, the Danish site states “reservations recommended” for the IC train departing Copenhagen. I’m wondering how important that would be and if it is, doesn’t a reservation mean I have to take that exact train at that time? I’d prefer not to be tied to that one reservation time. But, I also don’t want to stand the whole trip. Do the IC trains always recommend reservations or is this particular journey to Aarhus popular enough that the train is always full?
They always recommend reservations on IC trains, so there's nothing special about it - and you shouldn't take it too seriously, but Copenhagen - Aarhus is probably the busiest IC-route, as it connects the two largest cities in Denmark - but the trains are not always full (thank god!).
Yes, a reservation is indeed only valid for the exact train departure you buy it for (and if you get an Orange/Orange Fri ticket, those are also only valid for the selected departure too).
If you travel during rush hours or other popular travel times (such as Friday afternoon/evening and Sunday afternoon/evening), you should get a reservation, as trains do get busy. If you travel with a lot of luggage, you should get a reservation too. ICL/Lyn trains generally have more passengers for a longer part of the route than IC trains - and reservations are mandatory on ICL+/Lyn+. And if you want to be certain you won't have to stand up (because sometimes it's difficult to predict how many people show up to a particular departure time), or travel with several other people and want to sit together, you should get a reservation - but you got get your reservation closer to the departure, maybe even on the day you're travelling, if you want to keep some flexibility.
Thank you - your response has been extremely helpful.