It does do something buddy... good question too.
I'll try and explain this.. as simple as possible.. but from the question you asked, I'm thinking your an intelligent person so you shouldn't have any problems understanding what I'm about to explain to you.. and everyone else that cares to read this. Let's get started..
Darkness before harvesting your buds.. (I give my plants 36 hours of darkness personally) which is what I suggest to anyone that asks me.. but lets stay on the subject here... Darkness before harvesting your plant(s).. gives the plant(s) time to use up and nutrients/water that might be in the soil.. and in its root system (its roots). Not giving your plant(s) plenty of a darkness time.. will and can result in having buds that will taste funny and possibly even smell funny.
Why you might ask?
Well its simple, during the dark period of growing or what I call (sleep time)... your plant's roots thrive & grow. This is also where Photosynthesis comes into play.. which is where the plant uses up all that energy from trapping light into its leafs.. and uses this energy to sustain its life. It's how the plant lives..
But to sum this up for you.. in a short summary:
You should give your harvest ready plants.. 36 hours of complete darkness (to avoid THC breakdown as also). Why? because not doing this can cause your precious buds to smell and taste funny (smelling & tasting like nutrients.. or just not good at all) Why? Because, again, when you don't give your plant(s) that 36 hours of darkness.. your not giving the plant a chance to dispose and use up how ever much nutrients and water that the plant may still have in its stems, leafs, and of course.. its roots. And so when you just decide to harvest your plant(s) without doing this.. and just decide to harvest the plant... and dry your buds.. you will have buds (that you spent alot of time and energy on) that will smell/taste like crap.
So therefore.. giving your plants this 36 hour dark period before harvesting them will really help in aiding in the quality and taste of your buds. I know from experience.. My first grow taste like crap, but then again.. I didn't know about giving the plants the dark period before harvesting her. lols...
Live and learn.
Flushing your plants helps too... this will also help rid of any nutrients that may still be lurking inside the soil some where.
Hope this helped you some.
If not, my bad. Peace.