It's not really for the savings, as he already said, so much as for the conceptual purity. The only reason to use a block here is parsing rules. I can say something like

@username = map scalar getpwuid($_), @uid;
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The only reason I can't say

@year = map (localtime $_)[5], @timestamp;
# "Not enough arguments for map at line XY"
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is parsing rules. Using a block just because this is parsed slighly differently than the first example basically feels like a kludge, like clutter. It's like saying

print do { (localtime $timestamp)[5] };
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instead of

print +(localtime $timestamp)[5];
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Makeshifts last the longest.