Why does “Add to cart” function reloads full catalogue of products? Giving a huge delay on each product added to cart.
It doesn't. It does an ajax request to add the item to the cart and then updates the cart container with the resulting cart contents.
However, ajax request in cs-cart are fairly expensive in that they require the entire registry to be loaded and much other overhead as well that may not relate (like the PDF engine, a variety of addons, etc.).
That is response from CS cart support.
[quote][size=4]When you add a product to the cart, it takes a lot of time as well, because [size=5]the page content is reloaded in full[/size] after the product is added to the cart. It is required for updating content in dynamic blocks such as the cart content block.[/size]
[/quote]
So customer is waiting a lot if he wishes to list lots of products on a single page. And is waiting same full page reload on each add to cart.