Hi
Have tried to grow these in pots for several years with mostly bad results. while it can be kept at a very small size it didn't flower and the normal growth habit is spreading. This is an enormous ,fast growing tropical and seems to require a large size to do well.
At the opposite are dwarf poinciannas, will flower at two feet, can be pruned to almost any size and shape.
Much better choice for pot culture. gary

I have one ,and already its showing bonsai form with leaning trunk,reduced leaves. Im sure the leaves will get larger if left alone,and thats why I intend to pinch them.
If its healthy,cut it back. If you plan to always keep it potted,treat as you would any long term potted tree. I've cut back Albizia,in ground and in pots, like crazy-they never die.

Do me a favor-Google "Bonsai royal(at this point it finishes it for you!) poinciana",and you will see some great looking plants.
btw,do it in the images tab,and there is a young potted plant cut back hard-just as you asked.