The humble Vigil is a ship with two potential tasks. Tackle. EWAR.
It has the highest base speed of any non-pirate frigate, and a surfeit of midslots and a target painter bonus. In fleet situations, you would load it up with EWAR - TP's, TD's, damps, etc. You would use your idiotic speed to keep out of tackle range of your foes, messing up the enemy, and that is about it. Like all Disruption role frigates, it is more cost-effective to use this boat than any other ship, if you want to TP stuff.
For tackle, you want to put on a web and scram, and run down...well, basically anything. You also have a base scan res in excess of 1200mm with one sensor booster - basically an instalock. So you can use it for gate camping. It excels as a tackle frigate.
It is not a DPS boat - even with 2 rocket launchers and a
drone, you get about 58 DPS. Enough to take down a buffer armour
Harbinger, lets say, at the extreme top end - assuming you have the
luxury and time to do pull this off.
A third task presents itself, mostly as a subset of the Tackle genre. In an era where people use boosts as a way of, I quote "levelling the playing field of the small gangs versus the blobs", the Vigil is the only frigate which is both innocuous and - without boosts - capable of catching enemies such as Hookbills with boosts.
Fit right, the Vigil is a dangerous way of stopping kitey nanofag dampy frigates who try to peel off the enemies one by one from the group, or kite at 28km with light missiles, picking them off one by one. With 5.3km/s overheated, you can be a real threat to these guys, all for 8.5M ISK.