For the past 5 years, my female roommates have all had the bra struggle.
Trying to be a supportive friend, I always had to reassure them that they're breasts don't look to big in that shirt or no, I can't tell you aren't wearing a bra.
These ladies tried to go a whole week without wearing a bra and I can hear my college roommates screaming NOOOOOOO.
I pretty much don't have anything there (A cups let me here you holler!) so for me, it doesn't make a big difference between wearing one and not wearing one.
I have certain dresses that make wearing a bra difficult so I just go without, no hesitation.