Is it performance improvement to use unbound expression in array iteration?

Question

Assuming elements in list may be added or removed but element properties stay the same, is it performance improvement to use {#...} instead {!...} ?

In below example, it is decided that title prop is not going to be modified:

<aura:iteration items="{!v.feedItemList}" var="feedItem">
    <h2>{#feedItem.title}</h2>
</aura:iteration>

Answer 1

Yes, it is a performance benefit to use unbound expressions whenever possible. From the release notes:

Use the {#expression} syntax for unbound expressions when you pass an expression from a parent component to a child component, unless you require bidirectional data binding. Bound expressions with {!expression} create a bidirectional data binding that’s expensive for performance. Bound expressions can also create hard-to-debug errors due to the propagation of data changes through nested components.

In this case, using the unbound expression syntax will result in a shorter rendering cycle. Note that, as you've written in your example code, the items parameter must be a bound expression or the list can't be updated.