What happens if I delete used cache I've read this Mac OS X daily article, and now in finder I can see all the cache folder/files sorted by size:  



The problem is that I don't which cache is still in use from my applications, for example I don't know what is com.apple.helpd used for. So the question is: can I safely delete any folder? Or instead I risk that an application goes to search from these folders and maybe it crashes?
Nothing at all. Any caches that are required will be recreated at next reboot. I clean my caches once in a while as an OCD thing, but it's not needed. A cache is just a temporary file. If you delete it, the apps will recreate them when needed.

Caches were needed back in the HDD days to speed up loading in applications. On SSD's they're not as important, but they're legacy and probably won't go away anytime soon. You can keep deleting them, but they'll always come back. Don't worry about anything going wrong. A properly written app is smart enough to not actually save any settings in a cache so you won't have to worry about losing information.

Delete them all if you want. The ones your apps need will just be recreated. If you're on a HDD you'll notice slowdown for a while as apps recreate the cache. But on an SSD you won't notice a thing.