For those of you in Europe and North America, even in Japan, you can hear many signals on 30m because you have a much higher density of CW operators. With simple and modest stations, single or double hop propagation still produces good signals.
For us in some other parts of the world, we are very thin on the ground for CW ops. With D layer absorption and less than ideal F layer propagation, signals are attenuated before they reach us.
For this reason, the QTT Centre of Activity frequencies are really very helpful for those of us in the less active parts of the world. So as not to be stuck on one frequency that may be subject to QRM or primary service users (at least in theory they may pop up and have priority), so the idea is that the QTT centre of activity frequency varies each day.
It is the UTC date = khZ from band edge. So, today is 15th, so around 10115. Myself I park my RX (often with narrow filter when local noise levels are higher) on QTT CoA plus 300Hz, so today that is 10115.3. I do this because on 30m (as on other bands) most CW are on .0kHz, which are then busy, while few stations are using the large available spaces in between.
This way too, if I hear a signal exactly on frequency, I know it likely to be QTT i.e. non-5NN activity! You too may want to use this system, with the same, or a different offset, which you may want to advertise in your Email signature or web pages etc.
For those in Latin America, Africa, Asia and Oceania, looking for QTT, you will find this idea will help you — already here in VK every day several of us are making easy contact by having this daily changing frequency where we can park our RX while doing other things, or call CQ.
For those in Europe, Japan and North America, have a listen out on QTT CoA frequency of the day, and call CQ listening out carefully for us. We are very happy for the QSO!