Friday, Saturday, and Sunday are the big departure days from all the major starting points. That means the SJPdP bubble hits Pamplona about Monday night; hits Puente la Reina on Tuesday, Estella on Wednesday, etc. The last 100km from Sarria gets jammed with mobs departing on Saturday (Friday of a holiday weekend). Friday and Saturday are the big arrival days in Santiago.
Plan accordingly.
I was planning to post this additional information too, but falcon269 beat me to it.
I will add from own experience is that I agree that many people start their journey on the weekend, ( the end of the week, work is finished, retirement party over, etc) hence the reason flights cost more than Tuesday through to Thursday...
Hence the first wave of pilgrims, especially those from far away places like Canada, the USA, Australia, etc, arrive and set foot in Europe, late Saturday, and promptly start walking the next day, granted a bit jet lagged and tired. European have the home town advantage and are usually there late Friday night, bushy eyed and ready to roll. So the entire mob of pilgrims - first the Europeans and then those non European English speaking types climb and descend upon Roncesvalles over the weekend.
I am sure Roncesvalles in one busy crowded place during the weekend. By Monday as falcon269 has suggested Pamplona is over come with "what the heck, is it always this busy?" pilgrims. The wave continues to roll down the Spanish countryside until some get wise and decide to hang back a day or two, and let the wave pass them by. Other start putting in 40 km days and try to outrun the wave.
One approach to take is simply hang out in Saint Jean or Pamplona for the weekend ( or Paris ) and watch that first wave head off and up the big hill. Don't forget to say Buen camino as they pass you by. By Monday sleepy Roncesvalles is back to its normal self - sleepy. And the folks in Pamplona will waiting patiently for your arrival and you will be one of those lucky few writing in saying " I walked the entire route to Santiago and never had any problems getting a bed"
Just a thought to consider...