I've always been very sensitive to life in general, including insects/all animals. Ever since I was a kid. I've made a conscious choice not to kill bugs whenever possible a long time ago.
That said, my current criteria for killing or not killing a bug is: if it's inside my house and and I can't take it out (which I often try) and it can potentially harm me (kill me, or pass disease), or the ones I love (including my dog), I will kill it. Bugs that bite remain alive in my house as long as they mind their own business. I often have one of these in my house and don't kill them:
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(and I've been bitten by one once, although not inside my house).
As compassionate as I want to be, I'm not gonna put myself or the ones I love at risk. Ticks, for instance. My dog got ticks once and it was a nightmare. They give disease and crawl from the dog up to the ceiling and furniture and all sorts of places in your house, to then go back to the dog and complete their cycle. This poses a health threat to both the dog and humans living in the house. So, these, don't get to stay in my house no matter how compassionate I want to be to all life forms. Spiders are usually safe, though, unless they are poisonous.