Because we don't know the guage of the feed wire (wire feeding into the fuse box). Watch the video and you will understand the concept of overload.
You are adding a Dashcam with a drawer of less than 1.5a, it is very very unlikely that you are going to overload a feed wire by adding that.
As suggested previously, get yourself a multimeter and search around for suitable fuses. You will need fuses that are a suitable distance apart so that you can fit the tap into.
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