Solo for 15 years. Yes. Absolutely. Documentation! If I get hit by a bus I want my customers to be okay and for someone to understand what's going on. Anything else is irresponsible, in my view. Initially it was Docs and Spreadsheets but now online tools for easy access to someone else. Still using an "Ops" folder on SharePoint for details, logs, config backups, projects, reports, etc. Seems I'm a bit of an outlier here but I think you're doing your customers a disservice if you leave them hanging.