My bikes tires are always pumped up and they last me well over a year with absolutely no consequence from being pumped up, storing it pumped up will have absolutely no ill effect.
However, storing it upright with a flat can flat spot a tire.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1