The caster can reform a single regular-sized spider web in any way desired. Besides cleaning up for the squeamish, one could span a web across a room and create a nearly invisible, non-magical way to detect if someone entered it. Or create a nice little surprise: "There must be powerful magic at work here - look at how those spiders made their webs!"
In another application, the caster can learn from a freshly disturbed web, how large was the one that disturbed it, if there were more of them, how long ago it was, and so on.
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And you wondered why these wizards never bother to clean up.