Several of the games that I enjoy have various challenges and missions that come up every so often. They usually involve standard game play and provide some sort of reward.
Occasionally however the challenges encourage you to try techniques or strategies that you may not normally use.
My example here is going to be World of Warships. In World of Warships you basically have 6 ways to deal damage to enemy ships. You can hit them with your main guns, torpedo them, ram them, have your secondary guns deal damage, cause flooding or fire damage through one of the previous methods, or if you are using an aircraft carrier you can have various aircraft attack the enemy ships.
Main guns are the standard way to deal damage and usually the safest. They have the longest range and require a bit of skill at long range so it rewards higher skill play. Torpedoes are super powerful, doing tons of damage in a single hit. But they are short range, can usually only be fired to the sides, and can be dodged pretty easily if you aren’t close. Getting close usually means you are taking a ton of damage from your opponent as you steam towards them. This is just standard game balance. High risk, high reward.
When something high risk like that takes some practice to get right, sometimes you need to add an extra reward to get players to practice it such as a mission or a challenge. For example you get extra in game currency if you sink 5 ships with torpedoes.
This is also true when buffing or nerfing items, guns, or other abilities in games.
If you have a weak item that nobody is using and you give it some more power to make it playable, it is still hard to get players to use an item they have been trained to see as weak. So offering a reward to complete a challenge with it will allow your players to feel good about using it and trying it out again.
If you have an overpowered item and you take its power level down, when players find out they may stop using it even though it is still a viable item. Again you can use the challenge and reward pattern to get more people to use it to at least test its playability.
Keep getting wiser, stronger, and better.