I used circles on flies for chum. The idea was to reduce body/fin snagged fish and it did. Any snagged fish could be released by simply giving slack.

I landed four that were all hooked inside the mouth. The first was buried into the roof of the mouth. But, there were a lot less hookups so it probably makes flossing less successful.

Based on a couple years fishing them for pinks and chums it seems that, on flies, circles reduce the snagging a lot but also reduce total hookups.