This question is related to this one, but is a bit different.
In the layout (archive page) for a Wordpress project I'm working on right now there's a couple of image sizes that do not appear anywhere else. They are quite (by tens of pixels) close to the sizes that we already have registered — let's say, we have 210x300 already and the new size is 230x300. There's also another new image size which doubles that in height and could be also replaced by an already existing image size.
I know that having a lot of differently sized elements might not be good in terms of design consistency — so that could be one argument against it.
But, looking more from a practical side, are there any performance related concerns in adding more and more image sizes via
add_image_size? Currently we have 8 custom image sizes, and I'm not sure whether it's optimal to add more of them.