Explain bucket-to-bucket transfers

[iffy]

No description provided.

[iffy]

Imported from https://trello.com/c/hcRYXPBF

[mattlcook]

Does this mean there is actually a way to do bucket-to-bucket transfers while only typing the amount once? I can't seem to figure it out without typing a negative amount in one bucket and then a corresponding positive amount in another bucket. Maybe this is the design intent.