If you want to start initive when you smell a foul odor or hear distant talking (not just through the door you are standing at) you would be a nervous wreck. A DM should have little things scurry all the time. Then rolling initive gets real old real fast.
If you heard the creatures, then you are on guard. Rolling initive is a tip off, just like asking players to roll listen checks. There would be little to no chance of ever having a combat that can surprize the group, which means that your uncanny dodge wouldn't come up, or your good initive rolls. Then you are wandering around with +6 AC all the time. That gets boring, and an invisible wizard with Ghost sound could play with you for hours.
Initive should be reserved for when you have a definate threat. If an arrow flies out of the darkness, even if you can't see the enemy, you roll initive so you can take cover before the enemy shoots again. If you see a hiding monster, you roll initive. If you hear something behind a door, you roll when you open the door, because you won't be surprised by the enemy but they might not be surprized by you.
If you heard the creatures, then you are on guard. Rolling initive is a tip off, just like asking players to roll listen checks. There would be little to no chance of ever having a combat that can surprize the group, which means that your uncanny dodge wouldn't come up, or your good initive rolls. Then you are wandering around with +6 AC all the time. That gets boring, and an invisible wizard with Ghost sound could play with you for hours.
Initive should be reserved for when you have a definate threat. If an arrow flies out of the darkness, even if you can't see the enemy, you roll initive so you can take cover before the enemy shoots again. If you see a hiding monster, you roll initive. If you hear something behind a door, you roll when you open the door, because you won't be surprised by the enemy but they might not be surprized by you.