What are the pros and cons of having multiple co-advisors during a PhD?
The number of advisers you have really is a scenario-by-scenario issue. For example, during my PhD I had three advisers. However, only my primary supervisor was involved with the day to day aspects of my research whilst the other two showed up occasionally and asked some questions before disappearing for a few months again.

I do know of other cases where students have been split 50:50 between two advisers which also means two labs and two offices with them jumping between both trying to keep both happy because the two advisers don't talk very much.

It all depends on the research you're doing and the expertise of those around you. I imagine that in most cases, your primary adviser is enough but there are definitely cases, for example in interdisciplinary research where the expertise of an adviser from a different field would be very handy.