With the Amasty Improved Layered Navigation extension, it is possible to enable multi-select for the category filter. Enabling this feature changes the mechanics of the category filter.
A category filter without multi-select works as a redirect to the category page. It is impossible to deselect the filter, only click go back in the browser.
The multi-select category filter works just like other filters, it can be easily unchecked:
Nuances that may arise due to this difference:
SEO
If there is a need to use the SEO-friendly URLs, a category filter without a multi-select is a better option, since multi-select will put GET parameters in the URL disregarding the SEO settings.
Custom Pages (Facets)
Sometimes it is needed to access facets of the child categories from the parent category. Though it is possible to add the facet to the parent category as well, this won’t work with multiple facets. For example, if we have a Parent category (Bottoms) and we’d like to access individual custom pages which are displayed if we pick certain attributes (color: Gray) on each of the child subcategories (Pants and Shorts) the multi-select prevents us from doing so.
A category filter without multi-select will function as a redirect. Thus, if we pick the bray color on the parent category (Bottoms) and then pick the Pants or Shorts category in the category filter, we will be able to access the unique facet.