What is the purpose of the sword of memory reorganization and exchange in the sword world?

There are three sword-changing forms in the memory reorganization of the sword god domain: R2, R3 and R4. A full-size R3 exchange sword can be evolved into R4 with three R3 exchange swords (R2 needs two). In the exchange of weapons stores, when you use four r4 weapons, you can choose one R4 weapon for exchange, and only one weapon can be exchanged. If you exchange again, you need to wait until this weapon reappears in the exchange column (after exchanging a weapon, this weapon will disappear in the exchange column). It seems to be a loss to exchange four r4 for 1 R4, so it is more cost-effective to exchange with the sword of exchange. Of course, R4 with lower BS can also be used. Generally, R5 does this. Exchange swords have low attack power and poor combat skills, and are generally not used to equip characters for activities.