Question about Bard Instruments.

[Twilight-Sparkle]

So far I've been able to play every song just by singing, even the ones that say they require an instrument, like Hymn of Restoration. I have 4 instruments in my backpack but none of them are seeing any use. So mainly my question is how exactly do they affect a song? If I were to use a lute to play Hymn of Restoration instead of just singing it, would it heal more? Are there songs that absolutely require an instrument to use?

Also, when/if I acquire the Singing Short Sword, will I ever need to carry instruments with me again?

Thank you very much for your time and insight; I appreciate it.