Neutral Density Filter

I ordered a B+W 6-stop neutral density filter, 58mm filter ring for my Canon 50mm f/1.4 lens.  My first neutral density filter, goes with the tripod.  I'll try it out this weekend. I'll learn...

Upadate #1: the 58mm filter ring also fits my 85mm f/1.8 lens. 

Update #2: why do DSLRs need/use neutral density filters anyway?  You'd think that you could just do the ND filter electronically, probably getting higher quality. Indeed, point-and-shoots, at least some of them like the Canon G series, have a neutral density filter in the menu settings.