The big drawback for me with chemicals is the time involved to treat the water. I know ideal situations say the water is good to go in 30 minutes, but realistically the water is probably a bit colder and dirtier than the ideal so I would have the tendency to allow the chemicals to work for closer to 4 hours (the time needed for the 4 degree C, dirty water).

I know people that exclusively use chemicals for their water treatment and the best method seems to be to start treating the water before you need it. This assumes you have multiple water containers and as you empty one, you fill it with local water and throw the chemicals in. Then, by the time you need it the water is good to go.

With regards to boiling, the big drawback for me is that typically you want cold (or at least less than lukewarm) water to drink and cooling down the water after boiling it isn't a quick task.

When I was researching a backcountry water treatment solution for myself, I decided that full purification was what I wanted; I wasn't comfortable relying on filtering alone. I know viruses are a lower risk in North America, but I wanted a solution that could handle both bacteria and viruses.

Ultimately I decided to make my primary water purification system a SteriPen Journey with a pre-filter. This allows me to clean a litre of water in under 2 minutes which is good enough for me. For backup I also have MicroPur tablets and, when backpacking at least, boiling.

And, as Mark M mentioned, this method (perhaps more than others) does necessitate a backup. I ended up getting a defective SteriPen unit which failed in the backcountry. Backups kicked in and it was all good.

Even after getting a replacement SteriPen, they are definitely more sensitive to cold than I'd like so while I am still going to give it a shot this year as my primary purifier, I won't be without backups!