Boiling water does "cost" something- fuel, which also weighs something, perhaps a bigger pot, and time, which may be short.

I use chlorine tabs and sometimes take a small Sawyer Squeeze. I only purify drinking water- about 2 liters per day, not cooking water. It takes some practice to figure out a routine with chlorine tabs because they take 4 hours to fully purify, half hour for partial purification.

I am lucky that most places I backpack have good water and I do not even purify at all much of the time. It is all a matter of risk reduction - not a 100% necessity. A few swigs of less than ideal water have not seemed to caused any problems.

I have a steri-pen but have not used it. I do not like the idea of carrying batteries.