I personally prefer to have LSM for several reasons (Just my personal observation)
1) if you grow the LSM well, you'll vitually eliminate the blue green algae (green slime) from overtaking the top of the media
2) LSM seems have some anti fungal properties, plants grown on it seems to be healthier
3) LSM can be use as an indicator to check whether the media is getting too dry.
4) esthetically more pleasing
Please feel free to add points of the advantages of growing LFS with nepenthes. Thanks.