I have an old grunt call, I think its a Knight and Hale. I use it starting late pre rut, around here about Christmas time, on through the end of the season (31 Jan). I killed my biggest buck ever, came charging into the call in relatively thick cover, at 19 yds, unfortunately, w/ a rifle. He would have made Pope & Young easy if bow killed, but fell just short of Boone & Crockett.
I have also had a number of immature bucks come in, posing, looking for action, but not really aggressive. Years ago a pal lent me a cassette tape and I learned a call sequence that I pretty much have stayed w/ since.
Two sort grunts (trailing?) and drawn out tending grunt, then a short one again. I call VERY softly in most circumstances. The series takes about 10-15 seconds. I do it every 20-30 minutes if I don't forget. I also do it if I hear or see deer in the distance, or deer "noise". The bruiser that came charging was tearing a tree to pieces about 75 yds away. I heard the racket, called and he came running.
I have a can call, and sometimes combine the two, but no success w/ that. Somewhere I have a verysoft bleat call, that drew a big doe intobow range in early season a few years back, seemed liked curiosity more than anything.
Glad you inquired, I need to find that bleater and take it next time out!
I look at them as another tool/tactic. Try not to get carried away w/ them and use sparingly.