I checked for Plagiarism (Similarity Index), when I submitted my Thesis. Lo and behold, the report came with one similarity index to a work claimed by a stranger in another country. It was my initial PhD Proposal submitted to the Committee. Objectives, Research Questions, and Conceptual Framework among others. Not sure how that came about, when it was my entire work that I have not uploaded online.
From then on, I realised that it is worth the risk of self-plagiarism to upload own work online rather than be unhappy about plagiarism your own original work that has been stolen by others.
This is especially important for new post-graduates who tend to worry about publishing papers and uploading work online. Concern for self-plagiarism is minimal compared to finding out that your work is used by someone else without your knowledge.
Anything worthy of sharing is to be shared, with acknowledgement to its origin.