There are occasions where it is preferable to cut out freehand. Usually when you are cutting out very small pieces of card such as the station vallance shown below which can be a fiddly job.

In such cases I prefer to use a single edged razor blade as it is fairly firm and you can apply pressure directly over the tip. You will find these being sold in art shops or decorating shops. The great thing about this type of blade is that you can re-sharpen them on an oil stone thus extending their life, and saving you money.

Another excellent knife for freehand cutting in the Stanley Knife which I have used for years.