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.
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; if the pilot is competent, they'll see the laser and dive out of the way with a barrel roll. Trick them into doing so by aiming and charging, then shutting the weapon down and waiting for the roll to end before firing again.