On the level The Covenant on Halo 3, save the Spartan Laser given at the start of the level - or the spare reload lying nearby - for the Brute Chieftain in the Barrier Tower, as one/two hits (depending on the difficulty) should kill him. Hunters and the War Chieftain in the final tower are also good targets for the remaining charge.
During co-op in Halo: Reach level The Pillar of Autumn, it is advised to have one of the players concentrate fire on destroying Phantoms with the Onager while the other player(s) destroy Banshees with the Spartan Lasers, as Phantoms are difficult to eliminate with the laser due to their durability, and Banshees are difficult to eliminate with the Onager due to its slow turn speed.
In Halo 4, the Spartan Laser appears only in the mission Composer, found in an area where the last groups of Covenant are fought, including Banshees and Wraiths. If the player chooses to go on foot, grab the Spartan Laser to deal with the Wraiths from afar.
In Glassed, the Spartan Laser can be used to destroy the Phaeton required for the Iron skull found only on Legendary difficulty. However, the Laser takes two seconds to charge, which can result in the player missing the Phaeton and subsequently missing out on the skull.
In Evacuation, the Spartan Laser can be used to destroy the attacking Phaetons towards the end of the mission.
In Genesis, the Spartan Laser should be used in the Warden Eternal boss fights, preferably the first one. One or two hits coupled with a few hits from either the M820 Scorpion's cannon or a Type-58 Wraith's plasma mortar (especially the Ultra Wraith's) will bring down a Warden.
When coming upon a laser pick it up and get to a good/safe spot that vehicles go by often so you can get many vehicle kills. Wasting the laser on single infantry targets is a waste unless there is absolutely nothing else to shoot at on the map (or you happen to be armed with an Endgame in Warzone, as its lower damage, higher charge speed, and higher ammo count make it an effective anti-infantry weapon).
If an enemy is approaching you while you have a Spartan Laser and your death is inevitable, try to waste some of the battery power, so the other team doesn't get too many kills with it.
It would be better to use the weapon when hidden as it takes a long time to charge, and the targeting laser sight can be seen from across the map, drawing enemy attention to you.
In Halo 4, having the Ammo tactical package will allow any Spartan Laser the player acquires from a random spawn or a personal ordnance drop to have six shots instead of the standard four. This can be exceedingly devastating on vehicle-heavy maps with excellent sight lines like Ragnarok and Exile.
Warzone provides two even more lethal variations; the Ultra-Rare Endgame at REQ level 5, which has an extended magazine and shorter charge time, but less damage per shot as balance (best utilized against infantry for quick, brutal one-shot kills), and the Legendary Selene's Lance at REQ level 6, which has a similar charge time and moderate recoil but is unable to pierce through multiple targets at once, although it counters that by delivering a blow that can obliterate almost anything in its scope and a targeting laser that does damage while aiming. Slap on a Damage Boost to completely incinerate anything you aim at.
If aimed correctly, one Spartan Laser shot can take down a pair of Hunters.
Be careful when targeting enemy Banshees or Phaetons; if the pilot is competent, they'll see the laser and dive out of the way with a barrel roll or teleport away. Trick them into doing so by aiming and charging, then shutting the weapon down and waiting for the roll or teleportation to end before firing again.