I usually expect my PCs to look after their gear like the professionals that trained warriors and experienced hunters are. They don't have to spell out every time they use a whetting stone, change their bowstring, or look after their arrows' fletching.
However, I do include strung and unstrung bow "conditions" in my game, and usually reserve the right to make a call whether an archer's bow would probably be one or the other at the time. There have been situations in which it was unclear (travelling overland for long stretches, but with lots of known wildlife hazards about, or sleeping in a cave where a certain likelihood of wandering monsters could not be denied), where I let the player make the call.
There are no rules for what happens if a bow is strung for too long in my game, so there's no rules-enforced "risk" involved in just leaving the bow strung. But my players will still comfortably tell how they unstring a bow after a combat encounter, or when going to rest, or when stowing the weapon. They expect me not to punish them for that particular bit of realistic description, and I won't, usually. In fact, if a combat happened right after, my group and me would probably just feel that's bad luck/a matter of unforeseen circumstance/the bad guys seeing an opportunity and taking it/etc., not as "punishment" or DM dickishness. That's basically how our RPG-pseudo-realism works most of the time: describe what makes sense, and live with the consequences as you would in the real world.
Now if one player would explicitly tell me "I want to leave my bow strung all the time, for the whole two-week trip, because I just fear ambushes that much, even though my bow won't like that", I'd probably make something up on the spot, tell the player the likely mechanical consequences (which he is clearly expecting, given the way he's describing his actions), and let him/her decide whether to do it that way or not. A seasoned archer can make an informed decision in these circumstances, and I wouldn't take that kind of choice from my players: run the risk of finding myself weaponless, or permanently damaging my equipment: which is worse?