Two main reasons:<p>1. You can detect very common errors (e.g. typos) at compile-time instead of <i>maybe</i> detecting them at run-time. This makes the code much much more reliable (or equivalently you don&#x27;t need to do nearly as much testing).<p>2. Dynamic typing prevents IDEs from doing extremely useful things like <i>real</i> code completion and symbol renaming.<p>If you&#x27;re thinking &quot;but I edit Javascript with code completion&quot; or &quot;code completion isn&#x27;t such a big deal&quot; then it&#x27;s probably because you&#x27;ve never used <i>accurate</i> code completion, e.g. Microsoft&#x27;s Intellisense for C++, or pretty much an Java IDE.