Originally Posted by Taon

The crafting essentially has you saving some gold at the expense of total exp:

L5 Manyu = 720 exp
L20 Manyu = 1800 exp
L100 Manyu = 4800 exp

3 L5 Manyus: 1 L20 Manyu is a loss of 360 exp.
3 L20 Manyu: 1 L100 Manyu is a loss of 600 exp.

But, it costs less gold to fuse one Manyu compared to three of them; if gold isn't an issue, then the only other purpose would be to consolidate for storage. Sure, the crafting will be a QoL change, but it doesn't seem to be that huge of a deal to me.

Seeing as the Blooming itself consumes quite the number of gold coins, I find the option to save some rather nice.
Also the leveling up feels "faster" to me when its done with the L20 manyus once, instead of twice/thrice with the L5 ones. This is especially true the higher you climb on the current LVL.
Plus the option to make extra space when necessary is also quity handy.
Overall its a good function and I think many people would find it worthwhile, since I know for sure there are some guys here who are hardcore Inventory shuffle mages, unwilling to increase their space, thus having to play that Diablo-esque Inventory Tetris all the time