A mini marker is required to play the game of disc golf in professional play or tournaments, and even in casual doubles settings. Mini markers are used to mark your disc so that you may remove your previous throw from the ground and either use that disc again or use another of your choice.
Mini discs are cool because you can get a unique swirly one like the galactic ones or something with the SDG logo. The Sonic Jr's are great because they are a much smaller mold version of the sonic, a popular putt and approach disc.
Minis are also useful if you have a small basket. Sometimes it's just fun to throw a mini and see how you do with it. They're popular with children who love something that's their size, and they make a great stocking stuffer for the holidays. They're low price and they fit in your pocket easily. There are so many combinations of colors and stamps and dye jobs so be sure to find one that you love today.