SRAM 10sp shouldn't need the cassette spacer. Depending the Shimano cassette you had before - it may or not require. Just put it on without first and make sure (carefully) that:
1) You can tighten the cassette locking ring OK
2) Your derailler alignment is fine at lo and hi points.
Usually if you need spacer it's because without it, you can't get enough derailler 'reach' to shift into the smallest cog , and / or - at the largest cog you might risk running the derailler cage into the spokes.
For example - DA hub w/Ultegra Cassette -Spacer = YES, SRAM 1070 - Spacer = NO (at least when I set up some like this) YMMV according to your particular drop-out design and of course wheel build.
The sky above the port was the colour of television, tuned to a dead channel.
William Gibson; Neuromancer 1984. Although I had to admit that I had to google it to confirm my gut feeling. My Friend Jire wrote the first book in German about the cyberpunk literature movement in the eighties: