It's likely they are talking about lead set ups which release the lead when you are playing a fish, or, in the event of it getting snagged in heavy weed etc. It 's possible to set up inline and swivel type leads to achieve this effect.
Personally I have never found the need to dump the lead when playing a fish, I use inlines for nearly all my fishing, including in heavy weed. Perhaps I'm just a bit cynical on this one as most of the setups were devised by companies who sell leads... at anything up to a couple of quid each.