As in any type of control structure. Mustache is explicitly a template language without control structures. You can technically implement if/else statements and for loops using Mustache's sections, but you can't have expressions in your if statements. Template languages like Twig are more like an actual programming language.
This actually seems like a point against Twig for me. I really hope we don't introduce yet another programming language and added complexity on top of our already extremely complex stack....
That said I'd hope whatever solution we go with can be slotted out by 3rd parties in favour of another templating language.