I'm sure the choice of covering basslines as per recording has been covered many times but aside from simply wanting to put your spin on it (I most often do), there is the fact that I play in a 3 piece band, sometimes covering songs performed by 5-6 piece bands is 'potentially' fraught with difficulties. I sometimes ape the rhythm guitar part, maybe the keyboard part, possibly even horns etc. It would be to the detriment of the song to stick religiously to the original.