So here's something that's been worrying me for a while:
Would you say it's better to throw new enemies at a kill-team as soon as you think they can handle them, or would you rather keep some enemies up your sleeve so that the players don't face every threat the galaxy has to offer right away?
An example:
The way my players are going I could throw a few Chaos marines at them and be reasonably sure of avoiding a TPK. However, it's still early days and the characters are all still Rank 1. I would like to give them some CSMs to fight as an end battle for their next mission, but on the other hand I feel that having the players kill a few CSMs at Rank 1 takes away the fear of seeing them at later ranks.
How do you guys handle this kind of thing?