The key difference between Smart Filters and Regular Filters in Photoshop comes down to editability.
Regular Filters: When you apply a regular filter to a layer, it permanently changes the pixels of that layer. This means that if you later decide you want to adjust the filter settings or remove the filter altogether, you can't. Your changes are "baked in."
Smart Filters: Smart Filters are applied non-destructively to Smart Objects. This means that the filter effect is stored separately from the original image data. You can go back and adjust the filter settings, change the filter, or remove the filter entirely at any time.