It provides a simple way to creat chords and variations.
GarageBand '11 does not have the smart instruments you have on the IOS devices, but you have many, many loops instead, that already play chord progressions. The loops come in families of related loops, and you can easily transpose the loops in the track editor to play a progression C, G, F or similar.
Can the IOS chord sequences be uploaded to OSX GB?
You can import GarageBand for IOS projects in GarageBand on the Mac by sharing them to iTunes. The will be converted to the format of GarageBand '11 and you can continue to edit them on your Mac. It may sound a bit different however, since GarageBand on the Mac uses different instruments.
Only you will not be able to send the projects back and forth. The sharing is only one-way: iPhoe to Mac.