When a new wave of demons is in the process of spawning from an active Fade Rift, certain abilities like the Mage's Dispel, or the Templar Warrior specialisation's Spell Purge will insta-gib any demons they hit if they land before the demon spawns. Clearly this has the advantage of making the wave easier to deal with as you get fewer enemies spawning (or none at all in some cases). However, does doing this also have any disadvantages associated with it? For instance, do I get less XP? Less loot? Can I miss out on any Codex entries?
Alternatively, are they any reasons why I might not want to gib demons in this way and to just let them spawn?