What are the advantages of using DAD (diode array detector)?

[isuphysics]

what are the advantages of a DAD compared to a UVdetector?

[zokitano]

You can scan your analytes' spectra in the desired range of wavelengths in the UV/Vis region and therefore choose an appropriate detection wavelength for your analytes (often it is the wavelength for which the molar absorption coefficinet is largest -> greatest sensitivity in quantitative determinations)

Regards

[unmgvar]

if you need to do R&D work then it is good to have a PDA as zokitano stated, and also check for the specifity of your method using peak purity analysing tools in the software
on the other hand if you will do methods that were already done then it will simply be a less sensitive detector with features that you will never use that costed you more