https://en.wikipedia.org/wiki/Track_transition_curve
There is no operational disadvantage, it mitigates the appearance of the train "slamming" into the curves.
A common 180 degree spiral easement in "O" and O-27 that I have used is O72-O54-O42-O42-O42-O54-O72.
The disadvantage is that they require some extra planning for the space needed.
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