1. What do you do (e.g., checklist of your trip/route planning activities?)
I try to plan at least my longer trips the winter before, mostly to get an idea of how much food to dehydrate for spring/summer/fall--running the dehydrator on a 100*F day in July is no fun! I find an area I'm interested in and do some research. I may start with area online forums and websites just to get an idea of what's there and what it looks like. In the Pacific Northwest, those are portlandhikers.org (which has an excellent Field Guide), nwhikers.net (Seattle) and wta.org (Washington Trails Association, which has a hiking guide similar to the one on portlandhikers). Often this is all the info I need other than topo maps. If I'm going to a different region, I may get a trail guidebook for the area (great for daydreaming!) and will certainly get a larger scale trail map for planning (such as a USFS map of a specific wilderness area). Once I've narrowed down to a specific trip, I'll print out topo maps that cover the trip. I then work out a tentative itinerary based on such items as distance, elevation gain, water sources that show on the map, potential camp sites. I try to plan at least one layover day to allow for contingencies such as horrible weather, blisters, sick dog (I had to abort a trip once because he kept on barfing), or just wanting to spend an extra day enjoying a particularly beautiful spot. This tells me how many days I need. I plot the number of days into my handy-dandy master gear list, which I tailor to the specific trip, and print it out. I also print out the itinerary to give to a family member just in case.
2. How much time do you spend on it?
Probably too long! Planning is half the fun of the trip, particularly on a dreary, rainy January day! For some trips, it's months of daydreaming and reading of maps and guidebooks. For others, I may decide a few days before (whim, "always wanted to go there," interesting-looking online trip report), print out the maps and checklist, and go.
3. Why do you take this approach?
Meal planning--I try to plan, dehydrate and prepackage my meals the winter before so that at trip time I can just grab the needed number and go. I've never quite gotten to this point, but I try! For each trip, I want to take the meals I need and no more.
Gear planning--I check off the items on my list, load the pack and go. I'm old enough that I need to do a thorough job of this, so I don't find out in the middle of the trip that I've omitted something essential due to a "senior moment"!
Itinerary--since I backpack solo, my family wants to have some idea where to send SAR in case I don't come back. This keeps family off my back! I don't necessarily camp at the places noted on my itinerary (in fact, I usually don't!), but at least the route is the same.
4. If you were to totally ditch any sort of route/trip plan, what would be your main concerns with doing so?
I wouldn't ever not make some sort of plan, just because it's half the fun of the trip!
The two main issues are where to go instead of the original route and notifying the family member who has my itinerary.
On a trip to Wyoming a few years ago, a forest fire closed part of the area of my trip the day before I left (I didn't find out until I did a last minute check late in the evening). I tossed my guidebook and maps into the car. In the motel that night I figured out a replacement trip in about an hour and then called the designated family member with the new itinerary. I enjoyed the replacement trip as much as I would have the original! Since then, I've always had a "Plan B" for all longer trips, and take the needed maps. This is mainly a problem for trips a long way from home. I'm familiar enough with my own region that I can change at the last minute, as long as I have the maps and can phone the family.
I try not to change a route mid-trip because of the emergency issue. Two years ago I did have to turn around and go back out the fourth day (the barfing dog problem) of a one-way trip. That was the last time I planned a trip with no layover days! I now plan a bail-out route or two, which I note on the itinerary. If I think I may vary a trip, I will list possible choices on the itinerary.