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Full user review
"Peace of mind for the security conscious."
You will find out if someone is trying to talk to the network covertly. Since that's the main point of malware nowadays, if any of that crops up on the Mac then you'll probably know.
Quite a lot of effort to set up initially.
If you've found Little Snitch because you're looking for this sort of tool then grab it - it's well implemented, occupying a minuscule amount of system resources, and seems to catch things reliably.