When I owned Lionel's O27 switches, both 27" and 42", I rewired them for constant voltage. I found 2 advantages:
1. As already mentioned, the switches switch reliably regardless of track power.
2. Another advantage which I use often is that you can switch the switches without any track power applied. This is handy when setting up situations ahead of time or when you realized that needed to switch a switch but didn't have time, so you stop the train and can still switch the switch.
BTW: i also added electronics to my 42" ones to stop the buzzing. I don't know if what I was taught would stop the coils from burning out if a train was parked on it for an extended time, I'm not that gifted electronically. Bob Nelson provided the information to me on how to do it. It was expensive for me - he had the parts on hand and he's smart enough to know how to interconnect pieces. I'm not. Possibly other components (aka, cheaper) could have been used, don't know. I could have gotten the supplies on-line but had to buy a rather large quantity to get a good price. Since I was only doing 6 of the 42" ones, I wasn't going to buy 100 of each component! Especially since I didn't know for sure the results. I did the Radio Shack retail store route - not cheap. But it worked - no buzzing!!!!!
I wrote an article a few years back that I submitted to OGR on how to do this. They never published it (claimed it got lost in the transition of ownership) but I have emailed it to over 100 people. Email me if you would like the article and accompanying pictures.
Again I will repeat: I taught myself how to wire them for external power by reading. But it was Bob Nelson who drew up the schematic for the buzzing solution. I don't want to take any credit for something that was his idea.
- walt