It is both. Depending upon your weather, seasonal closures/openings and freedom to fish. An example of late for me: I have recently spent more time researching patterns I had fleeting chances at last year and was not prepared with the right patterns and/or correct presentation (Yellow Sally Stonefly, Sculpin/Streamer Patterns).
You fish and see you need to figure out an insect for the next time (what was that large, yellow, fluttering fly popping out of mid-stream? (Mayfly, but it looked like a Stonefly?). Or, you are still cut off for the season (weather, closures, work, obligations). You plan for the time span you will have to fish and study the hatches you will experience on the bodies of river you will most likely visit (example: August-October for Crooked R., Deschutes R., Metolius R., McKenzie R., Tunkwa L., Leighton L. etc.).
This is part of the ongoing fun of tying and fishing (or, fishing and tying).