Isolation amplifier has an amplifier and isolator in one package. The reason of using isolation amplifier here is to minimize return loss and amplify the power at the same time

What is the reason to use an isolation amplifier?
I am working on a circuit  connected to computer  with FTDI FT232RL. The circuit have got some op-amps and one MCU. Total power consumption (including FTDI chip) is near by 80 mA /h (at 5V). My op-amps need well regulated 5V power (single supply). Here comes the time to design power supply. 
USB Vcc pin is connected to the FT232RL Vcc and MCU's Vcc. The question is this how i should use USB's Vcc pin? 

First connecting USB Vcc to LDO regulator IC like AMS1117 and powering both FTDI IC and MCU + Op-amps with AMS1117's regulated output is good?

USB Vcc-->AMS1117-->FTDI chip+MCU+Op-amps 

Or connecting USB Vcc to FTDI Vcc and a regulator IC on the MCU +Op-amps  is good?

USB Vcc-->FTDI chip-->AMS1117-->MCU+Op-amps 
