+1. Another use of type systems that often falls under the radar is as documentation. Coming back or ramping up in a project that's typed is much more straightforward than one that isn't, for a few reasons:

- Types are documentation most editors will allow you to click through, which makes finding definitions much easier, as opposed to just comments.

- Types are documentation that's enforced by the type checker, meaning it's always there. Either the type checker can infer it, so the editor can display it even if the developer didn't write it, or it can't, so it asks the developer to write it.

- Due to the same enforcement as above, types are documentation that never grows stale.

Add to all this the fact good editors can parse and understand this documentation, and use this and provide code suggestions, etc. and it's IMO most often a very worth investment.