You can use it either way , pl can log and show display also . I use both and the pl comes with the update chip to make the SM to sample up 15 times faster
You can use the Powerlogger without the Scanmaster, but why. Leaving the Scanmaster out of the picture and you're forced to use a laptop ALL the time, if you want to see any data.
The afr or o2 and kr and mph when it happened is all the SM will recall , all the logging will be on the PL, if you logged it and saved it so you could review it later on the PL console