Having good documentation is great, but there is nevertheless a substantive cost in high turnover even if you have good documentation. Documentation doesn’t replace experience with the product or project, nor is it ever complete.
Looking back at my own career, I do not jump ship every 18 months, and I have been able to accumulate deep knowledge that are broadly applicable, that has enabled a lot of options when it is time to go to a new company.
So in addition to having better continuity of institutional knowledge, there is a benefit to staying on longer (at least for me).
