found this, hope it helps
When to use a low-value range
There is no time when an exclusively low value range is optimal. The purpose of including low value hands in a range is to extract additional value from high value hands, or to play more hands in general against opponents that fold too often. In the first case, you need high value hands in your range to make the strategy work. In the second, there is no reason to limit yourself to low value hands.
When to use a high-value range
Against loose-passive opponents, who will play most hands and take them to the river, you will want to play high-value hands. Since these players can't be bluffed, you need hands that can get to showdown and win. Your "high value" range can expand to include some medium hands depending on how light opponents will call down (if they call down with any pair, hands that make second pair can be played profitably), but it will not include low value hands.
This is the best strategy against a level 0 player.
When to use a polarized range
As your opponents become more able to fold hands in certain situations, it becomes profitable to start adding bluffs to your range. When adding bluffs to a range, it is best to start with hands that have little-to-no showdown value - the 72o-type hands. There are a few spots this can be applied. A polarized range can be used when 3-betting in position pre-flop against a good opponent. A good opponent will not call with many hands out of position - they may have some high value hands in their calling range, but for the most part they will 4-bet or fold. In this situation, you will either want to get your money all-in, or fold. You go all-in with your high value hands, and fold the rest. So if you 3-bet with a hand like AJs, but have to fold to an all-in, that is a waste of a hand that can be profitably played in position. This is why we polarize our range - when we get 4-bet with 72o, and have to fold, we aren't losing value.
A similar place where a polarized range can be useful is a flop check-raising situation. When the board comes out K 8 4 rainbow, and you check-raise, you are representing a very strong range - mainly sets, possibly AK. To balance that range, you can add hands like small pocket pairs or missed suited connectors - these hands have little-to-no value against the range that your opponent will continue with.
This will be the best strategy against a level 1 or level 2 player.
When to use a merged range
A merged range comes into play when your opponent starts adjusting to your polarized range. On the previous flop of K 8 4, an opponent may start adjusting to your polarized raising range by calling down with second pair, or a pocket pair like 99 or 77. Suddenly, we can start raising hands like KJ and QQ for value. A merged range will put opponents to many more difficult decisions, which will likely lead to them making more mistakes.
This strategy will be best employed against higher level thinkers, where there are significant meta-game factors and constant adjustment of ranges as the match proceeds.