Generally speaking that isnt good practice but if it works go ahead, over time the buzzer may not start up with resistance in series.
A piece of tape over the hole is a convenient way to quieten a beeper.
This thread is about a pot but your schematic does not show the pot and does not show how you connected it.
Resistor R2 does not show its resistance.
Pin 2 is the trigger pin on a 555 but yours is connected to nothing. Interference picked up by the pin 2 wire might trigger the 555 to turn off the LED and beeper.
Pin 6 is the threshold pin on a 555 used as a timer but yours detects darkness to turn off the beeper.
The switch does not turn off the circuit, just the LED so the battery will slowly run down.
Generally speaking that isnt good practice but if it works go ahead, over time the buzzer may not start up with resistance in series.
A piece of tape over the hole is a convenient way to quieten a beeper.
In the beeper there is a driver circuit, this will have a minimum voltage supply, this will be the quietest the thing will go while operating it within the manufacturers ratings.
If you were making a production run you'd go for a different beeper.
You could try using Pwm to control the volume but that would make your circuit more complex.
sudo apt-get install wine*
winecfg #(set up wine)
wget http://ltspice.analog.com/software/LTspiceXVII.exe
wine LTSpiceXVII.exe #(this installs LTSpice)
#you should now have LTSpice in your dropdown menu under the "other" or "miscellaneous" submenu