Many factors at play here..is the bow laminated or solid one piece wood...
some solid bows can lose poundage or see limb warp if left strung...most modern laminated as a rule are safe to leave strung...but why might be a question...
Some points are strung its a weapon...unstrug its a stick...lol
Strung there are more chances of someone dry firing the bow, string getting damaged...etc
if you shoot every day there is no issue leaving it strung ...if its
Some bows can get damaged by stringing improper so maybe better left strung...
if proper methods and bow stringers used...like mentioned it only takes seconds...and in my eyes a fun part of shooting recurve or longbow...part of the ritual that makes shooting fun...
JMHO
Neil