If you are developing a big application, managing large templates can be difficult. The QWeb template supports subtemplates, so you can divide large templates into smaller subtemplates and you can reuse them in multiple templates. For subtemplates, you can use a t-call attribute, like in this example:

<template id="first_template">
    <div> Test Template </div>
</template>

<template id="second_template">
    <t t-call="first_template"/>
</template>