3-rail track power - why?

[Mobi]

Lionel uses 3-rail track power in O-gauge trains.

Is there any advantage? I can see reverse loops are easier.
ChatGPT says 3-rail system is more reliable than 2-rail because current has more paths to complete circuit. Is that true in real life?

Also, O-gauge is typically used indoor. Do people with 3-rail run trains outdoor?

As a disadvantage, it must be costlier than 2-rail tracks as it uses more metal? In addition, these locos are incompatible with 2-rail tracks I believe.

 

[maxi-model]

Possibly an early manufacturing dictate. With a 3 rail system you do not need insulated wheelsets if your centre rail (3rd) is live and the running rails are the returns. Then cheaper and simpler to produce. UK's Hornby Dublo (OO) system, originated in the 1930's used 3 rail. Most 1:1 electric railways use rails only for return and a live 3rd rail or overhead wire for current. You could mix old steam locos with modern electrics on lines with mixed traction. Also a handy way to "lock" the buyer into your system, a marketing ploy. One that any manufacturer worth their salt ditched decades ago. Even those who make live steam locos (insulated wheels, that is) Max