I dont't switch. 1 breast is more than enough for my baby per session. I will alternate at each session, i.e. 1st session, drink from left breast, 2nd session drink from right, and so on. If baby wants more like during growth spurt, I will offer the fuller size 1st, then switch to the other when drained. I didn't pump inititally, only in the last month of maternity leave to build up my stash.