Reasoning
Character: Radimaji Undrwrldcub, Horde Troll Shaman, Elemental + Restoration, RP server. Leatherworking makes the mail caster/healer sets (Skycaller's for Elemental, Mender's for Restoration, Skirmisher's hybrid; skill 210-250, 60-90 Merchant's Favor), the Mystic Rugged Armor Kit (spell power) and the Camp Tent > Tanning Rack > Sewing Machine ladder (rested XP). Engineering adds the Reagent Bot > Repair Bot > Anarchist's Workbench camp line (reagents incl. Ankhs, and field repairs), goggles, Emergency Field Cloak, Stealthman 52, the Ultralight Goblin Glider, bombs and transporters. Warcraft Tavern's Shaman guide recommends this pair. Its claim that Engineering crafts Shaman Totems looks like an error: 4 sources put the Totem relics in Enchanting, so buy them from an enchanter. Trade-off: neither profession gathers, and the Druid (Herbalism + Alchemy) does not supply leather or ore.
Confidence note
Analysis built from sourced profession facts