There are no guidelines. It completely depends on your settings, the complexity of your garment, the baseline performance of your scene without it, etc. The only way you can really tell is to try it yourself. Thanks. The things is I wouldn't wanna skin and paint weight on my character without the cloth and later realize it's a kill for my machine and I would start thinking about detaching and reattaching and re-painting, you know. I know I'm being lazy but, I just thought someone might have an experience of how it affects render time averagely