enable ap

i have the e-tech ADWG02 with enable ap on,is this needed?
what happens when i uncheck this?

notebook is wireless and 1 pc connected with cable to modem.

i have 2 neigbours ( one computer nerd) wich show up in netstumbler but
are encrypted.
i tried to lower the transmitter output so the neighbours can't see my
modem anymore and unable to hack my modem....but even set at 12,5 % the
output is still -50db,not lower at all.
why isn't the output power lower?

thanks,andre