Skype on MacOS keeps 600Mb caches, are these both deleteable?
There's no need to delete these files, but there's no "harm" if you do.


The SKAvatarCache holds thumbnails of your contacts for quick access without downloading each and every time from the Internet
The media_messaging/emo_cache_v2 holds the animated emoticons for faster rendering.


You can delete, but these files will be recreated when you view and/or message with contacts.  It's nothing that should be of concern that would require periodic maintenance.