Is 'banking' items adding a lot of lv 1 to the same equipment?
IIRC 'banking' a bracelet requires around 19-20 bracelets from level 1
ie. LV 1 + 10* LV 1 = LV 22 [10 x lv 1 upgrade cost]
LV 22 + 9 or 10* LV 1 = LV 30 [9 or 10 x lv 22 upgrade cost]

However if you dont 'bank' and combine equipment like in the guides you can save exp and coins
Back to the bracelet example
Make 8 Lv 1 + Lv 1 = Lv 10 or 11(if you get a great synthesis success) [8 x lv 1 upgrade cost]
Lv 1 + 7* LV 10 & 1 Lv 11 = Lv 30 [8 x lv 1 upgrade cost]

As you can see the bottom method, it is cheaper in terms of upgrade cost, as all you leveling is done at level 1 and not at lv 22. Also we are only using 16 bracelets to max it as opposed to dumbly sending 10 at a time all level 1 into the desired equipment which would need around 20 bracelets.

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Make em like this