The only real objection to adjustable stems is weight. Some also have rigidity issues at the hinge, allowing some unwanted play, though better made ones are fine. The main reason not to simply leave it on is that's it's deemed uncool, and you might draw comments from folks who think they're better than you are.
Leave the adjustable on as long as possible until you're sure you've dialed in your position, then either replace it or don't depending on your mood.
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