Firstly, it takes a couple of days for the CO2 in the headspace to dissolve into the beer, cold liquid absorbs more gas than warm. You'll notice better head and tighter-beaded bubbles if you chill them for a couple of days.
If you can chill them for a couple of weeks, you'll get nice clear beer and even better head retention and foam as the protein particulates and polyphenols drop out of solution.
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