Why (why not) 3 engines ?

[leonard17F]

I hope I will not ask a very simple/trivial question, but why would you, as an operator/owner, prefer to acquire or use a 3-engine biz jet (let's say a Falcon 900 or F7X) as opposed to a 2-engine (F2000, G450, 550, etc...) ?
In particular, what would justify the potential acquisition/operating cost difference ?

[7xXx]

Already discussed here:
http://www.pprune.org/biz-jets-ag-flying-ga-etc/392596-why-do-dassaults-have-3-engines.html

bonne lecture