As a tutor marking assignments, I regularly come across cases of plagiarism. As someone who put a lot of effort into my coursework studies it really offends me to see what students think they can (and ultimately do) get away with - it's making me incredibly jaded about the way universities are run and the value of (my) degrees.
I spot things from the mild "sharing answers" to the "change a few things so it's not obvious" copying, to the virtually identical outright blatant copying (not even changing the student number) to the absurd "submitting a screenshot of last years solutions". Talking to other tutors I seem to spot and pursue a lot more than anyone else.
When I come across these I always examine them, make a determination if it breaches my threshold (usually a bit past the "just change it a bit" level), then pass it on to the lecturer for them to decide what to do. It takes be significant effort to do this - I might recognise an unusual way of writing something, then go back through the assignments I've already marked to check how similar it is, then I'll decide if it looks too similar, then send an email about it.
I can't remember a single case that has gone further than a warning (yes even the one who submitted last year's solutions). I care about this a lot and I don't want students to think they can keep doing this with impunity, but there seems to be a general reluctance in academia to do anything, even in extreme cases. It makes me wonder whether it's worth the checking, the discussing, the extra time that I don't get paid for and ultimately the emotional toll it takes on me. It would be so much easier to let it slide.
From a pragmatic perspective of (for want of a better phrase) cost/benefit, what level of plagiarism should I be bothering myself with? Should I just ignore anything but the most absurd cases?