I don't think the context necessarily prescribes either one. Mostly it would depend upon your approach to gardening, I suppose.
You also almost never plant all the seeds in one season, so you've usually got lots of leftovers. Then you've got to look at which ones are viable long term, and which ones aren't, and see what new ones if any you need to buy - all parts of planning before planting.
Part of my yearly gardening routine is pulling out my stockpiles of seeds, and planning what varieties to plant based on what I've got the most of.
I've also used a method called square foot gardening, which maximizes output while minimizing space, which requires a lot of planning regarding layout, spacing, companion planting, etc.
I used to whip up sketches for the layouts, and create schedules for planting additional harvests, timetables for starting seedlings and transplanting, switching from cool to warm season crops and then back, etc. It got to the point where I no longer enjoyed the planting for all the planning, so I decided to just go back to winging it.
I realized I'd gone to far when I started my gardening by firing up computer programs, so I no longer plan to that extent,but I still generally start with a rough plan before I plant.
I don't really follow it, but my mother still plants religiously by the lunar cycles. She still calls me to remind me that next Wednesday is the right cycle for root crops, or next Saturday is the next sowing cycle, etc. So she literally plans when to plant.
