It is to three bet with a less than strong hand. You do it to steal the pot and / or take control of the betting.
could you give a couple example hands and some methodology for doing this? based on what you've said i'd use a light three bet with.....idk, 10/J suited or A/2 suited? something like that where you have a bunch of live draws and the potential for live cards, or perhaps at a time when you know someone rarely 4 bet without AA/KK?
I just read a chapter about this in a book. To explain it to the folks, light 3-betting means re-raising a hand that is most likely to be weaker than the initial raiser's hand. In the book I'm reading it says 80% value 3-bet and 20% light 3-bet is alright. An example would be light 3-betting as MP (middle position) against UTG (under the gun) with 56s-QJs, because with suited connectors you will avoid getting second best hands (e.g. AK vs AJ) and you have good flop potential. Also A5s would block AA-AK combinations which could avoid a 4-bet.
It really depends on the villain's fold to 3 bet percentage. If they fold too often then I am going to 3 bet them most of the time. If they are calling stations I am mostly going to be 3 betting them for value.
Rather than calling it light 3betting id rather say 3betting a polar range and you want to use a polar range vs villains you have fold equity against.So you might 3bet a polar range against an utg opener with say KK+,A5s-A2s,KTs.Where as against someone who doesn't like to fold to 3bets you would use a linear range say JJ+,AQs+,AKo.
Then vs the regs who will be the Tag's and Lag's you have a mixed strategy combining the two previous ranges JJ+,AQs+,A5s-A2s,KTs,AKo, as we expect to have fold equity vs these villains but we dont expect them to be overfolding. You can look to 3bet KK+ and the bluff part of the range A5s-A2s,KTs wherever possible.And play a mixed strategy with the rest of the range with either 3bets or calls.
To work out a polar range just multiply your value range by 1.5 to give you the bluff ratio so KK+ for example for 12 combos would give 18 bluff combos.The linear range is just pure value hands which can widen more and more the fishier the villain.