rework

src/when_to_use_rust.md

@@ -4,15 +4,25 @@ Like most general programming languages, Rust can be used for virtually any kind
 
 Rust is designed for programs and projects where
 
-* performance;
+* performance and/or memory usage;
 * reliability; and
 * long-term maintaince
 
 are top considerations. If your program fits these criteria, then Rust would probably be a good choice. 
 
+## What are great domains for Rust?
+
+Domains where Rust can be a particularly good fit:
+
+* Systems programing, low-level development, or embedded systems;
+* Network systems, where Rust offers "predictably low" tail latency, low memory usage, and high reliability;
+* Developer tools and CLI applications, where Rust's can snappy response time and getting the right answer is super important.
+
 ## When not to use Rust?
 
 When there's a better option, of course! Here are some reasons you might prefer not to use Rust
 
-* you need to make use of a library in another language;
-* you want to deliver something as quickly as possible and you don't care how well it works.
+* you want to make use of a library or framework in another language;
+* you're targeting an environment or community where the other language is the default choice (e.g., Swift for iOS);
+* rapid iteration is more important than getting the details right;
+* you want to learn something else or you just really like the other language. That's cool too.