I asked this same question myself in the early days. Unless you are going to be away from bubs then no you don't need to.
And I was told by a friend who breastfed until their DS was 2 if I decided I wanted to express to wait until 6-8 weeks until my supply had settled. I had enough issues with leaking and huge/hard boobs in those early days without expressing and making more milk.
I have recently started expressing after feeds to have a supply in the freezer as I will be out for 3 hours one day for four weeks soon and will feel more comfortable knowing if DS wants to feed early and I'm not back he won't starve. Plus there is the fact I will have to return to work part time in the near future.
I use a manual pump because I don't plan to pump all the time but I find the washing and sterilising a pain in the a***. However dh hires the hospital grade electric pumps at work and just got one back in and I don't need to buy the kit that you use with it as he had some spare parts plus I can use some of the stuff from my manual as it's the same brand so I'm going to give it a go and see if I find it not do much of a PITA.
If you do choose to express and leave bubs with someone else with EBM, make sure bubs will take it before you leave them for your own piece of mind. We gave DS a bottle of EBM last weekend as a trial and he did not know what to do with it and had I not have had a second kind of bottle here or been home he would have starved.