RT-N66U - Bridge WDS mode

[kiat]

Hi

Can anyone please tell me what's the purpose of Bridge mode in RT-N66U means?

I'm currently using TP-Link TP-WA901N in wireless client mode to link 2 physical network together. In the TP-WA901N, they advice using WDS. If WDS is used the wired networks will be forwarded in the format of WDS frames consisting of four address fields.

Not too sure what this means. Is there any performance / functional advantage for turn on the WDS in both the TP-WA901N and RT-N66U?

thanks for the advice!!