Good evening my friends, thank you for granting me your attention on this bitterly cold night!

My question - my meta-question as the case may be - concerns the purpose of these words referred to as "tags". Let me be clear: I use tags. The site supports them, so why shouldn't I? But my understanding of their reason for existing is tragically incomplete.

Are they used for searching? Are they useful in any other way? Or do they merely act as decoration, adorning these questions like so many baubles on a department store Christmas tree...

Please, let me know!