What effect does having 'measured' as a parameter in additive white gaussian noise?
The answer is in the page you linked:


  out = awgn(in,snr) adds white Gaussian noise to the vector signal in. This syntax assumes that the power of in is 0 dBW.
  
  out = awgn(in,snr,signalpower) accepts an input signal power value in dBW. To have the function measure the power of in before adding noise, specify signalpower as 'measured'.


So if you don't provide this parameter, Matlab will assume the input signal power is 0 dBW, and scale the added noise to give the requested SNR relative to 0 dBW.

If you provide a numerical value for the signalpower, Matlab will assume that power instead of 0 dBW.

if you specify 'measured', Matlab will measure the power of the input signal and scale the added noise relative to its actual power rather than to 0 dBW or some other specified level.