The original concept was for them to feed off a persons sweat and perhaps body hair as well; which could prove advantageous to some people. I like the idea of them becoming parasitic and consuming healthy flesh if left in place for more then a week or two, especially if they execrate an anesthetic preventing the wearer from realizing they were being slowly eaten alive until they tried to remove them...
Also in the original post apocalypse setting their main draw back was the continual perception/skill penalty from feeling the creatures crawling over your skin, making it difficult to perform complex tasks and conentrate for long, let alone get a good nights sleep.
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besides the caused discomfort when set on, wearing clothing was difficult to impossible as well as the social interaction pentaly. (Who's going to have a normal conversation with someone covered in a crawling carpet of bugs, a few of which may decide you are a more desireable host?) This alone provided enough problems to off set their advantages and keep them balanced. (they also weren't very bullet proof, making them a less then optimal armor choice for firearms conflicts.)