There are two LV6 digimon that is most used in yellow deck, those are yellow ShineGreymon and WarGreymon from BT4. While ShineGreymon relies on number of yellow tamers, WarGreymon relies on number of security cards. By the way, talking about normal defensive style of yellow, WarGreymon is maybe the only yellow digimon that showing offensive move in the tamer battle. To use his main effect "when attacking", we needs to sacrifice one security card (put to hand), We may first thought it is not a good strategy to reduce the number of security card, it makes you lose the game faster, then why every yellow play still using it?
[BT4-048] WarGreymon is a LV6 digimon for yellow deck, he is normally using with Chaosmon: Valdur Arm. He is landed to the right color because of the ability to "Recovery" of yellow color. There is too many advantages that given to him from many other yellow digimon card or tamers. In this post, let me bring out a deck from Digimon Card Meta deck-list collection to talk about the support and collaboration to WarGreymon.
This deck is created by Suke, and it is just a normal yellow deck with strategy of recovery (defense) and WarGreymon build (offense). This deck uses 3 copies of [BT2-032] Salamon and [BT2-039] Magnadramon to get "Recovery" for security pile. All the LV4 digimon are cheap to play, so they can move to [BT3-039] Angewomon faster, the "when digivolved" effect is only valid when this digimon is digivolved in the battle area, not raising area. Angewomon really can help to delay to security attack speed of the opponent, and in next turn you can digivolve to LV6 WarGreymon. The Lucemon is put in 4 copies to play for free when Magnadramon attacking or digimon with LV5 Angewomon in its evolution source. When Lucemon plays from those effects, it also triggers "Recovery+1" for the deck, it seems a good strategy right.
WarGreymon, when he appears in the battle, whether moved out from raising area or digivolved from a LV5 in the battle, normally what they will do is: if the opponent have a rested digimon that have very high DP ( higher than 11000), we will put 1 security card to hand to reduce 6000DP to that digimon and destroy it by attacking either using this Wargreymon or other digimon. Tamer T.K Takaishi already helped to reveal all the cards in security pile, so making decision to take or not take the card is easier. If there is no security card left to take (or you dont want to take), then we can digivolve to LV7 Chaosmon: Valdur Arm to deduct up to 14000DP to one opponent's digimon.
The option card Blinding Light and LV3 Bushiagumon is game-ending or last surprised attack for yellow deck. TK. Takaishi reset 3 memory for beginning of the turn, then using Blinding Light option card to add 2 memory for the turn, then play Bushiagumon with "haste" to do last attack to win the game. The Bliding Light can still use even if there is no security left in security pile, that is a huge advantage. Even if we cannot draw the Bliding Light option card, we can also play free cost LV3 Bushiagumon by using Angewomon inheritable effect, so Bushiagumon is most likely the last soldier to finish the game. Sometime they use WarGreymon effect or Blinding Light effect to purposely drop the security card to 3 or less to trigger other card "recovery" effect or play LV3 digimon for free (from Angewomon inheritable effect).
To summary, the deck with WarGreymon gives yellow player a higher chance to win compared to other LV6 yellow digimon, it is easier to build a deck around him with a completed support. And with the first LV7 yellow digimon Chaosmon: Valdur Arm, the yellow becomes stronger and formidable in tamer battle.