clamsrus

First off.....the breast lymphatics drain several different ways......straight back through the chest wall, upand out towards the armpit and lymph nodes there, and finally towards the sternum and into the chest there.
Why does this matter??...because the pressure of lymphatic drainage is very very low compared with say the pressure in arteries or veins, and if you put the squeeze on the drainage the breast becomes engorged or swollen slightly, and like all good glands this is not a desirable thing full time.
Wearing of bras has been implicated in breast changes.....engorged tissue that doesn't clear waste metabolites properly undergo what are referred to as trophic changes and these are thought to be a probable cause of other cellular changes.
Now if you can imagine wearing tight socks continuously you might get the idea.
Guts of it is.....breasts like other bits of your anatomy shouldn't be restrained long term.....you don't wear tight jocks to bed......don't wear your bra to bed