Will my Shopify store loading speed be affected if I use Shopify apps?

Complexity can cause problems. The more apps you make use of, the slower your page will become. The slower your page becomes, the fewer sales you will make.

I would recommend that you ask yourself whether the use of a specific app is absolutely necessary to the function and success of your store before using it.

If I add apps to my store, but I am not using them, will they still slow down the page?

Inactive apps shouldn't affect your site speed, but I would suggest that you remove them if you are not using them.