My horrible story is that i worked for — hours in a row and suddenly... a blackout and lost those 6 hour of work. I know i was fool, but i think an auto-saving function could be a very good add on the incoming versions.
There's already one.
http://www.scirra.com/tutorials/269/keep-your-work-safe-with-construct-2s-backup-options
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OK... Sorry about my ignorance =/