In most cases, there is no reason to delete your own positive Ratings & Compliments.
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However, we have received (very rarely) complaints where some inappropriate positive Ratings were marked. Members have actually asked to remove a Great, etc. For example, the blog may be about some sad incident and someone mistakenly marked a Great. In such cases, ONLY the blog owner will be able to delete Ratings which he/she thinks are inappropriate.
Thanks.