I am using the TL-R605 (Gigabit Load Balancer) with 3 WAN connections with speeds 40, 10 and 5 MBPS (with 3 different ISPs) as connection WAN 1, 2 and 3, also I have set the speed accordingly in WAN connection.

Ironically, the WAN2 with 10 MBPS (WAN 2) shows maximum data utilization this has remained the same even if I physically shift the 10MBPS connection to WAN 1 (i.e. maximum utilization always remains with the 10MBPS connection). Apart from this there are no policy routing enabled to re-direct the traffic to any particular WAN.

This leads me to think that there's some algorithm which detects the network efficiency based on same parameters. 

I know that I can force the load-balancer to use the WAN ports based on the bandwidth (by enabling Bandwidth Based Balance Routing or BBBR) but I want to understand what drawback would it cause if I enable this setting i.e. BBBR.

Also, I have tested multithread download speeds by enabling and disabling BBBR, but in both cases I do get the same, total of all 3 WAN speed i.e. at least 55 MBPS.