You can sacrifice lands and pay a small amount of mana for various effects, like drawing a card or giving it unblockable
It is the combination with the on cast effects of the Eldrazi which make Shelldock so abusive when compared to the rest on offer

The deck: Simic Elf Tribal Comparative Analysis 34 Lands 15 Ramp : Galadriel of Lothlrien, Sol Ring, Arcane Signet, Elvish Archdruid, Elvish Mystic, Arbor Elf, Marwyn, the Nurturer, Elven Chorus, Rashmi, Eternities Crafter, Priest of Titania, Eladamri, Korvecdal, Elvish Harbinger, Planetarium of Wan Shi Tong, Scouting Trek (kinda), Wirewood Channeler 9 Target Removal : Reclamation Sage, Beast Within, Windswift Slice, Mystic Confluence, Dissolve, Chomping Changeling, Masked Vandal, Glorious Gale, Frilled Mystic 2 Board Wipes :Raise the Palisade, Devastation Tide 1 Graveyard Recursion : Mirkwood Elk 1 Graveyard Hate : Scavenger Grounds 3 Tutors : Prime Speaker Vannifar, Momir Vig, Simic Visionary, Elvish Harbinger 8 Protection : Heroic Intervention, Galadhrim Ambush, Mystic Confluence, Dissolve, Asceticism, Sapling Nursery (Treefolk and Forests), Frilled Mystic, Ezuri, Renegade Leader 15 Card Draw : Elrond, Master of Healing, Elven Farsight (1/2), Preordain (1/2), Opt (1/2), Birthday Escape (1/2), Tatyova, Benthic Druid, Staff of Domination, Eladamri, Korvecdal (kinda), Mystic Confluence, Lifecrafters Bestiary, Leaf-Crowned Visionary, Elven Chorus (kinda), Champions of the Perfect, The Temporal Anchor, Edric, Spymaster of Trest, Momir Vig, Simic Visionary,Rashmi, Eternities Crafter 6 Finishers/ Surprise /Alternate win conditions : Elvish Warmaster, Lost Isle Calling, Haldir, Lrien Lieutenant, Overwhelming Stampede, Ezuri, Renegade Leader, Galadhrim Brigade As we see form the comparative analysis, the rates per category are very good

Im confident Faith & Grief is the worst, even with the artifact support of the set