Why would I need to use a templating framework like Jade or Handlebars when writing client side apps using AngularJS.
I should say that I have never used any of these templating frameworks either. So I am not familiar with the advantages completely. But when I look at Handlebars for example, it does many of the same things as I would do in Angular, such as looping etc.
As far as I can tell, it would make most sense to create the templates in Angular using proper HTML and then do all templating client side, and combine this with an API first approach using node and mongo for example.
The reason for this confusion is that a lot of the examples I find on GitHub make use of Jade, and it seems counter intuitive for me.
Please enlighten me, and set me straight. I would love to learn some best practices from people who know much more than I do.
Those who unquestioningly favour Jade in an Angular environment fail to understand that view logic belongs on the client, and business logic on the server, just as the OP commented.
Don't do it unless you have a very good reason to do it. In engineering, a system with fewer moving parts is a more reliable system, and a system where interface boundaries (client/server) are respected is more maintainable over the long term, so default to the simplest architecture and clean division of labour if possible. If you have overriding reasons, do what you must, but caveat emptor.
Recently I reviewed some code where straight Angular templating would have done a far better job than mixing in Jade, just through maintaining simplicity.
Aside from template extension, Jade brings nothing worthwhile to the table that Angular doesn't already supply. Let's be honest: Using the sound principle of "favour composition over inheritance" (i.e. partials), you shouldn't ever need template extensibility. Jade is hardly "easier to parse" than HTML. They are but trivially different, while Jade adds another level of indirection - best avoided.
There is one valid, specialised case for server-side templating: Optimisation, remembering that premature optimisation is generally a Bad Thing. Where performance is truly at issue, and you have the server capacity to spare to handle this, server side templating can assist. This applies to products like Twitter and Basecamp, where the cost of doing a lot of server side work is offset by the gains of reduced requests to the server.
As for Handlebars, there is no need to replace AngularJS's (amazing) client-side templating.