I had a friend enthuse at me lately, because her campaign secrets came together and the PCs sat down and worked out what was going on, and made a plan.
I don’t have that happen so often, because I build campaigns differently to her. If there’s a thing that I miss about games, it’s that. She’s put in a lot of effort to pre-making it, and the players got to the big plot point, and worked it all out, and killed the person that knew a lot and then worked out that person would have been useful, and they’re going to deal with it and she was just eating popcorn while smiling through most of the session…
And I don’t get that.
I tend to make things up by leaving out a lot of hooks, some of which I have already developed, and some of which look unexpectedly shiny to the PCs and get developed because they show interest. It means I can go on with a campaign almost indefinitely, as long as everyone is still invested in it, but it also means I can’t drop hints and leave the PCs to work things out. I have a tendency to try to finish off every thread, because very few have greater importance than others, and that can also lead to long campaigns. My median is 2 years, playing once a week. In all that time, I’ve never put in a lot of effort up front for a campaign that went nowhere, and I’ve had really great times, but I’ve also never had those moments where the players look at the juggernaut I’ve released, and go ‘oh’.
I don’t really have an answer to this – there’s no question, because there’s no right and no wrong. It’s just up to you to decide how much planning you want to put in up front, and whether it’s worth it for you.