This paper, available at https://ideas.repec.org/p/hhs/hasite/0039.html, reviews the literature on the incentives of leniency applicants. It is a really useful piece for anyone doing leniency work, and extremely thorough.
It is not possible to provide a summary of the paper: it reviews too many papers and possible scenarios (the first section looks at economic models, the second at empirical evidence). If there is a basic argument underpinning all of this, it seems to be that incentives to increase cartel enforcement results may not be well-aligned with maximising welfare / may lead to excessively generous leniency conditions; and that leniency reduces collusion but that the EU is too nice to cartelists and extends leniency to far too many companies.