Back leads can be very advantageous in certain circumstances, particularly on venues that receive lots of pressure from anglers and you need to pin your line down to the lake bed. On such venues, any fish that bump into your lines, can often mean the kiss of death. To avoid this, it's best to pin your lines down. Yes, this can be acheived by using slack lines, but the big disadvantage there is that you will also lose vital bite indication. By dropping on a back lead, you can pin your lines down, yet still keep them semi-tight to register bites. They also minimise the chances of you catching your other lines whilst playing fish back to the bank.
The problem with most back leads however is that in the event of hooking a fish, they don't slide down the line very well, but we can assure you there's no chance of that happening with these!