The bottom line is that you must be capable of writing a cheque for a new engine, at any time.
Obviously you hope you don't have to, and statistically speaking that normally works out
But the value of a plane - whatever it is - hangs 100.000000% on its
continued airworthiness, and if you are unable to maintain that, it is worth scrap.
Anybody ignoring this is deluding themselves.
In the piston game, you need to be able to bankroll "suprises" of say 20k-30k. In the turboprop game, the figure is 200k-300k.