The use of crow calls and other locator-type calls to find gobblers is an art unto itself in turkey hunting. Gobblers are "wired" to gobble during the spring breeding season, mostly in response to other gobblers in competition for the hens in an area. They are so predisposed to gobble at the first noise that sounds anything like another gobbler, they will often come back on top of any suspect sound they hear that is of the proper abruptness and volume to trigger their gobbling response. We hunters have come to refer to this trait as "shock gobbling".
Using locator calls such as crow calls to find gobblers by getting them to shock gobble is a very effective tactic. There are some places and conditions where it is almost essential to success,...and by the same token, there are places and conditions where it is almost useless. One thing I can tell you is that I have never hunted anyplace where using locator calls at the right time at first light in the morning was not an effective method of locating gobblers. I have also hunted places where it was just as effective at last light in the evening, as well. And as you can tell by your own experience, there are times and conditions during the day where crow calls, as well as other locators, can be effective for getting a gobbler to give away his position.
Personally, I swear by using locators to find gobblers. I can state with some certainty that I have killed many birds by first finding them with locator calls, and I advise everybody to learn to use them religiously,....under the right circumstances. Like I said up front, locator call use is its own art,...just like turkey calling.