Grab any digital SLR, power it on and your instantly ready to shoot.
With mirrorless that is not always the case. Recently I saw an interesting video on Youtube looking at startup times for the Leica M 240 series.
Its often said format in camera, and the video demonstrated that a card formatted in camera compared to a memory card formatted on a computer made quite a difference to start up time. So first rule format in camera. If you have to format on the computer, download SD Formatter which will do it correctly.