I had no idea the Canon70d came with an sd card. But if you have enough money to buy that good of a camera you should make the investment of an extra sd card. Any good filmmaker always have back up, so if you have 2 sd cards if one doesn't work or something, you have another one. And the reason why it matters how you use it is because of the different formats, if you record in hd that will take up more space. If you record longer clips, it will take up more space. But overall, my advice is just to have two sd cards just in case, at least 16 gb in size. Sd cards aren't even that expensive, under $40, which is nothing compared to the cost of the 70d.