In the early days of modular psu's people worried that there would be voltage drop because of the extra connection at the psu/modular plug of the pigtail for various components. I think it's matured enough it's essentially a non issue and the benefit is only using the cables you need so you don't have a huge bundle of wires to try and shove someplace. Some are semi modular which can be the best of both worlds. A solid direct wired connection to the power cables you know you'll need regardless (motherboard 4+4 and 20-24 pin power connectors) and the peripheral cables are modular (for hdd/ssd, gpu, dvd/br etc).