You just have to time it right, not necessarily bad play, just a mistake. If W. USA is lightly defended, Alaska/W. Can/C. USA almost undefended and America doesn’t have any Armor in N. America (a situation I’ve seen a majority of the time) you could easily take it.
But even if America retakes, you’ve diverted assets, you’ve taken 13 IPC for 1 round, at least 2 the next round since America can’t possibly take W. Can, W. USA and Alaska all in the same round without naval assistance, and you’ve lost roughly 9 IPC in units, tops.
15 IPC for 9. Your transports arn’t out of comission, cause they just move back to SZ 60 after the assault to shuttle troops. You got 1 transport out of position, but hopefully that’s not one you need. (You only NEED 4 transports. more is desireable, but you only NEED 4.)
Besides, the manuever alone is worth the games you don’t get to do it!