I see people using the spoiler tag to hide large blocks of text and images. The blur effect is kind of annoying with a big chunk of content like that. You should probably use the details tag instead. It’s available under the little gear icon. It gives you an effect like this:
Summary
This text (or image) will be hidden
This is similar to the old spoiler tag on vBulletin. The blur effect from the spoiler tag on Discourse is best for short spoilers.
Discourse devs might want to add a nag dialogue box to suggest the details tag if people put a ton of content in the spoiler tag.