I'll be traveling on a Eurail Global Pass this summer. I'm experienced at it. I will be making a couple trips in Spain. I am aware that even with the Eurail Pass seat reservations are required on almost all Spanish trains. I have no pblm with that. I may take an AVE in late June between Barcelona and Llieda, mid-week, mid-day. I may also take an AVE between Llieda and Madrid, also mid-week, mid-day. I will not have tight connections anywhere. So how important is it, really, in those circumstances, to book a seat resv way, way in advance? Like, say, in the next week or so, for a trip in late June. How much risk am I taking if I wait till I get to the station? Is it likely I'd be shut out completely for mid-week mid-day trains between those city pairs in late June?
The risk is close to zero. Trains rarely sell out.
The risk is, likely, close to zero - but I have seen a couple and a single disappointed and overheard conversations of upset in thirty odd years. The couple were on the next journey two hours later, the single purchased a far more expensive preferente seat. It is not my way to not purchase in advance for peace of mind.