Is it a trip to experience new things? Is it a pilgrimage? These are only two possibilities. But they are sufficiently different to demonstrate my thoughts on this very personal and unique issue.
On the vacation / hike for fun side, plan ahead, at least a few days. Then you know nothing can go wrong…we know that’s not true…
If purely a pilgrimage, as others have said, go with the flow. If it is harder to find a bed, when needed, prepare to camp out or think outside the box. If albergues are full, consider an upgrade to a B&B or a hotel for a night. Maybe walk to a farm and ask to sleep in an out building or barn if they store hay/straw. That way there is no need for a tent, though i always carry a plastic tarp for emergencies.
Also, as mentioned, shorter stages means stopping earlier each day thereby getting a bed before most are still out there walking.
How your body feel about all this? Always give your body the deciding vote.
Head: C’mon, we can do another 25 km…and that will get us a whole day ahead of schedule!!!
Feet: Sure Head, you come down here where all of you hits the road and spell me for a while. Maybe if we can do that, we can do another 25 km. But I get to ride on the shoulders, not you…