filters - Simple FFT filtering vs. e.g. butterworth filtering

I am currently working on functional connectivity analysis of EEG, and need to bandpass filter my data into different frequency bands (Delta, Theta, Alpha and Beta). An important thing is that the filter doesn't cause phase distortion. I know a butterworth filter and processing the data in both the forward and reverse directions (e.g. with filtfilt in Matlab) is a good approach, however I was still wondering about the simple FFT/IFFT filtering approach. What are the exact disadvantages of this method? Does this method cause phase distortions? What are 'edge effects' that occur with this method?