I think Igncom1's notion was that it comes in, kills one enemy frigate, and then retreats, rather than dying...
...But I don't agree that's a good trade. The player is routinely outnumbered, after all.
(What I do find amusing is that, in the ancient days of Corvus, the Vigilance was actually my favorite of the starting frigates. But, uh, that was a time before ship systems, a time when pilums were actually good, and - for reasons that were never entirely clear - a time when the starting Vigilance variant came with 15 flux vents rather than the normal maximum of 10, all of which contributed to it being able to take on groups of three or four pirate frigates on its own. Which. Well. Nowadays, none of those things are true... and you don't generally see enemy groups as small as only three or four frigates, either. Typical enemy fleet sizes are a lot larger now than they were then, and I personally feel that the game's suffered for that.)