"Guidebook" is so pre-internet age!! We are seeking information of various types that formerly were found in guidebooks: trip planning, route-finding, distances, elevation profiles, alternative routes, bailout/shortcut points, accommodations, local services, cultural/history, spiritual guide, and diary.
Ten years ago I found
Brierley indispensable for all of those; now I believe there are better easier ways of getting the information. On my last short camino, seems everyone has a smartphone (on cafe stop 14 of 19 people were on their devices; so, since that is already on everyones packing list, I'd use it for information needs (unless you fear loss, breakage, etc of the device.
Trip planning--use this site, and the first half of
Brierley to learn about the ways of the Camino.
Route finding--not necessary on the
Camino Frances; it is so well (over)marked you cannot lose your way easily. Just follow the arrows. The exception this is in the larger towns. I have been lost in Pamplona, Logrono, Leon, Burgos, and Ponferrada; and even in the lengthy part of Castrojeriz looking for the albergue. And for me, google maps is not in my skill set--so I would love a guidebook of city plans!! Distances and elevation profiles do not require a heavy guidebook. The handouts at SJpdp are more than sufficient. I prefer the brochure from the association Albergue Red since that also has the premium albergue accommodations.
Alternative routes: not sure any guidebook is valuable here. Three that come to mind that require no guidebook are Napoleon/Valcarlos, San Martin/Marzarife, Samos/San Xil. A guidem ight be helpful on the Pradela/Montana out of Villafranca. (never walked but have talked to walkers who say it is not well marked). I come from a backbacking history and I would NEVER go off the main route with anything less than a full topographical map. Same for shortcuts and bail out points. (I carry a full set of IGN 1:100000) maps for LePuy tho; as I am not fond of the French routing aimed at weekend walkers and not long distance walkers who do not want an extra 2km to see something obtuse; and I refer to these frequently during the day.)
Accommodations and local services: these change so fast that a guidebooks are out of date. MiamMiamDoDo formerly was the best on accommodations. I am new to it, but Gronze was perfect for this last short trip. With a list of accommodations at each town complete with phone numbers it did everything but dial my phone and make the reservation.
Cultural, History, spirit guide etc: I loved
Brierley for this in the early years and there is some information on Mundicamino website.
Diary: use a notebook or a smartphone notetaking app.
So the short answer is 'carry no paper guidebook for the
Camino Frances". Download what you need to your smartphone and keep the SPpdp handouts handy for a paper backup. I would be inclined to take a guidebook for any of the other routes though.
Technology changes have made print media increasingly obsolete.