Clash of Clans has been running for a few years already but have been loosing their players drastically, until they have revived the concept of the Friendly Challenge. Back then, there was no way for you to prove to someone who sticks to their point of finding a rush base more beneficial because the both of you cannot test your bases of which one is indeed the best. Rush bases were popular on those days, of which leads to harder matches due to the high town hall level yet low defenses. So if you have someone disagreeing as to what you are doing, then it would be a simpler discussion, due to the Friendly Challenge.
Not only can you finally attack those towns of the players that you disagree upon but also, you can utilize the Friendly Challenge in practice games before attacking in the war battlefield. The good thing about the Friendly Challenge is that you get to keep the troops that you have used to attack, making the cycle a never ending one, or rather unlimited match ups. You could then discuss on the ways to improve your attacks, gaining feedback from other clan members, and getting to practice on them, for you to improve your clashing skills over time. This does bring a wild kick in the game as clans become more active as they want to take turns in giving a shot at it.
If you do have a friend that is quite a bully but in plain words, criticizing your development in Clash of Clans, before you two can spar, you have to be in the same clan. So that means, you would have to join his or her clan first, or either he or she must join yours.
Another thing most people are thinking about is the preparation of it on the clan wars. Some would opt to use this as an advantage by copying the enemy base and then try to practice on it using the Friendly Challenge to perfect the attack. Now this has been made sure by the creators of the game that there would be no issues like such so the solution that they had was to put a time lock on every edited base. Once you have modified a base of yours, you would have to wait for a day before you can have someone attack it. This disables players to do their practice attacks before hand.
The Friendly Challenge is one feature that you would surely want to try so if you have stopped playing the game for some time already, then now is the best time to come back and enjoy the many great additions in Clash of Clans.