Breast pump while breastfeeding

Mga momsh,sino gumagamit ng breast pump habang nagbebreastfeed? Yong expressed milk,bina-bottlefed nyo din ba kay baby o iniistore lang? 24 weeks preggy here on my 2nd baby,plan ko mag-breastfeed talaga kasi sa firsborn ko mixfeed eh,magastos kasi pag mix feed..