The Bard never goes alone without his Tunes. He can summon only four creatures to his party from one of the 16 tunes. Some Instruments gives him more Mana and add another room for him to summon. The Bard only has one room at the begging of the game but when you get some new Instruments you get more Mana and one of them gives out more room that'll reach to four. There are different types of tunes that'll help the Bard to continue in his adventures so they are very useful to them to be in your party.