I find that beyond this, not having a cognitive disconnect in working on the frontend/backend is really nice. And depending on your data tier(s), can even go there (Mongo, Plv8, etc).

Compared to when I'd have to use ActionScript, JavaScript, VBScript, VB6, T-SQL daily... that was sometimes painful... then adding C# and VB.Net to the mix was ugly having to switch from one area of code to another.