I agree with @parietal ’s distinction between niceness and fairness, OP.
When I am nice to someone, that’s my own choice, freely given. I do this with family, friends, neighbours, colleagues and strangers.
Beyond this, in my network of relationships I am looking for a sense of fairness. There is an overlap between the two concepts.
In HE, you may put out a call for someone to take a lecture in 2 days because you are ill. I know I have a conference in 3 months. I take your lecture, and I know your timetable is generally free for one of the lectures I’ll need cover for.
If closer to the time you make vague excuses I won’t be thrilled. If this is what you see as ‘leverage’, I would characterise it differently.
If we were close, no one else was stepping in and you were in danger of redundancy owing to health challenges, that would change the flavour. If you had a reputation for being too busy for reciprocity I wouldn’t have offered in the first place.
I also realise that your idea of leverage could be entirely different.