Celeborn is a staple in a silvan deck similar to Dáin Ironfoot for dwarves deck. Global buffs are rare abilities in a game and Celeborn ability is really unique and thematic way to play the game. Some will say it's worse off and harder to play as compared to Dain's bonus that is constant and not just limited to a single round. That is particularly true but there silvan allies have some unique abilities that synergise well with this Celeborn abilities.
Firstly, silvan deck required more micro management as you will see allies enter and leave play frequently to trigger their "enters play" effects. For that, you need few cards for maximum effect. Firstly, you need O Lórien! for discount of 1 for silvan allies. Next, is The Elvenking to ensure you can keep replaying silvan allies to trigger their abilities in the next round while maintaining the global buffs. Nenya
Let's try to see the effects of silvan allies 1) Galion. Now he will have 2W when enter play and you can return him to your hand in next round to trigger the effects again as he is 0 cost. 2) Orophin. It's a unique card you say, no more. Return him to your hand and you can trigger his effect again to return an ally to hand from discard to ensure you have constant access to ally cards. With discount from o lorien, 2 cost for 3W and 3S is nothing to sniffed at.
To truly unlock Celeborn abilities to next level, you will need his wife Galadriel to ensure allies don't exhaust to quest when enter play. Now orophin can quest for 3 and not exhausted so he has ranged attack of 3. There are many other different permutations and experiments here. Some will argue that Thranduil will be the third hero to complete the trifecta to bring solid defense and ability to play silvan ally of any sphere (albeit only in combat phase). This is not necessary imo as Legolas and Éomer provides better synergy and allow access to tactics sphere. Nenya already providers galadriel access to lore sphere so you have 4 sphere. This is to ensure allies can enter during planning phase and quests and not exhausted for defense or attack later. Have fun playing silvan decks.