add_image_size creating lots of images (of various sizes)

I wonder if its a good idea to use add_image_size or is it just a convinence feature. I say this as I think add_image_size creates images of various sizes regardless of what the usage if the image maybe

eg. I may want a thumbnail of 500×200 in my portfolio pages only. but WordPress will create images of 500×200 for all images I upload right? If I have a bunch of add_image_size, it will clutter up my uploads with useless images I will never use? Is there a better solution? Resize before upload, maybe alittle troublesome?

For image formats that are only used for a small fraction of the images, I suggest using an on-the-fly image resizer. Preferrably one that caches the images so that you only have to resize them once. I use TimThumb for a number of projects, and it’s been good enough for me.