In my experience the biggest retention issue is for an employer to deliver what was promised during the hiring process. Employers that are competing for talent are known to paint the picture of how they see their ideal instead of how things really are. This sets the new hire's expectations to an unreasonably high standard, and when those expectations aren't met they walk.
Being honest with potential hires and showing them both the good and the bad about what you have to offer may lose you a few good hires but will surely save you many more bad (short tenure) hires over time. As a recruiter, I hear the bait-and-switch cited by roughly 25-50% of job seekers that are leaving a company after a relatively short 0-3 year stint.
Most of the things baited and switched probably wouldn't be required to be put in writing or not, because they aren't legally binding anyway. Even if the legally binding things are put in writing, usually we're talking about at will employment anyway, so they could just fire you instead of making good on a 'promise'.
The types of things I'm talking about with bait and switch are related to what projects you will work on (say you will be put on Team X's sexy initiative, then on Day 1 told you that Team Y's maintenance isn't going well and your skills are needed there), what the future holds for the company (over-optimistic about funding promises, sales estimates, delivery dates, etc.), or how you will be able to progress.
Does the management team have a history of promoting from within or will they hire a former co-worker for the role you are in line for? Can you look at tangible past results and numbers as evidence.
It's not very likely to get these types of items in writing, and unless it's legally binding you don't have any remedy in most cases.
Being honest with potential hires and showing them both the good and the bad about what you have to offer may lose you a few good hires but will surely save you many more bad (short tenure) hires over time. As a recruiter, I hear the bait-and-switch cited by roughly 25-50% of job seekers that are leaving a company after a relatively short 0-3 year stint.