When you grow an apple for eating you want it to be big and juicy and to taste great the moment you pluck it from the tree.
However these desirable characteristics in an eating Apple are the polar opposite of what is wanted from a cider apple. This is the key reason why growing dedicated cider apples is a good idea.
Think about where the flavours are concentrated. Mostly they are found in the skin. At school we learned that a smaller sphere has a higher surface to volume ratio than a larger sphere. This means a bucket of smaller apples has more surface area (and therefore more flavoursome peel) than a bucket of larger apples. A large apple is not the best apple as far as a cider maker is concerned.
Of course we take what we can get and a crop of big apples is better than no apples at all.
Secondly, the flavour of apple juice and the flavour of cider are distinct. The blend of sweet, sharp and bitter that makes a cider so delicious can only be made in two ways. You can either blend a mix of cooking, eating and crab apples to approximate a classic flavour profile, or just use a dedicated cider apple as your base. Through many generations of orchard management, cider makers have developed apples that provide the depth and complexity of flavour in single varieties. So, in short, dedicated cider apples are less work.
Thirdly, there is less scrumping. If your apples are small, ugly and taste almost inedible when plucked, you will lose fewer of them to passers by who fancy a nice free apple.
In short, my advice is do yourself a favour and plant some heritage cider trees this year.