Stickying is the most effective method of bringing a post to the attention to the board. As such, some people ask for a sticky, if they think the post has high value or high potential or is of some high tier value.

It could be that the meme is particularly poignant, the ideas provoking, the link is noteworthy, or the post hits the target for whatever reason. Sometimes a post is stickied by mods simply to raise attention to it. Essentially, a sticky is NOT an endorsement. Sometimes something that needs to be pulled apart or blown out of the water is stickied.

Essentially, a sticky is a "Look Here" marker. People will call for it, or a mod will execute it, if they think the post is noteworthy.