Dotted-decimal notation is used to display IP addresses for easier reading by humans. Each of 4 bytes (8 bits in binary or 2 digits in hexadecimal number) is represented by a decimal number (of which there are 256 possible combinations, 0-255) and then seperated by decimal points. For example, a typical IP netmask is

11111111111111111111111100000000 in binary and 0xffffff00 in hexadecimal. The binary is certainly cumbersome and hex is not terrible, but when you have something like 0xa4ee21b3 it can be a little confusing, especially to people unfamiliar with hex. When you display this same value in dotted-decimal notation it looks like 255.255.255.0. Still, it could be a little confusing to read (again with something like 240.142.42.21), but it's a big improvement. That's why it exists!