Well, if you are using the query caching or image caching then leave it of course.
If you have a high number of images I strongly recommend not deleting it, as it saves lots of performance. If most of those files as images that it means it saved extreme amounts of bandwidth, because it served these cached thumbnails instead of the full sized images.
If you however don't want to use that cache, you can update to the latest version, which has a feature to disable the image cropping function and it won't generate any thumbnails. The downside is of course, that the results will display the original sized images scaled down to the thumbnail size, which means much more bandwidth.Best,
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