Such type of conjunction allows to increase the highest possible discharging. For example, you use 30 A storage battery, but in mechanical box for two storage batteries you can count on 60 A, it means that the termination will distributed among them equally.
Also the capacity increases. For example, if you use two 2200 mA storage batteries, the general capacity will be 4400 mA, which cannot but please us.
We have to mention and one point of great nicety. Many people are aware, that a big contribution to the common voltage slump is made by storage battery slump (while using the mods with minimal slumps). As a rule, the less resistance is (the strain is heavier, because while resistance is decreasing the discharging increases), the more storage battery "settles" and gives fewer resistance. In this case the load divides among the storage battery, so slumps get smaller. You possibly have met not once just odd huge boxmods with 4 or more storage batteries. From the standpoint of ergonomics it's much uncomfortable (the size often really impreses), but slumps under parallel conjunction in such devices are really small. Let's determine minimal acceptable resistance for parallel conjunction, ignoring accumulation slumps under load: devide strain (4, 2 V) into highest discharging (2 storage batteries 30A+30A=60A) and we'll get 0, 07 Ohms. Further take the square of resistance divide into strain and get 252 W.