I've found if I put an echo infront of a distortion, i and turn it up, i get feedback, and its not the jay farrer kind - its a nasty digital unmusical sound. I guess it matters to a certain extent, if you put a delay before a distortion it could get pretty ugly... but beauty is in the eye of beholder. Typically effect chains are something like this: Compressors>Distortions/Fuzzes etc>Time Based Effects (eg reverb, chorus, delay, echo) ...but messying around with the order may produce some cool tones this is probably why the reverb tank is the after the effects loop on all amps
