When mixing and storing polish or gel, you have 3 options, a surface (palette) a funnel, or both. In most cases you must remix small amounts that you throw way or fill an old polish bottle. Mixing in bottles provides no visibility and usually results in an overflow. Palettes and funnels waste your time and money. After mixing, product is left in the funnel or on the palette. These tools are commonly made of plastic as well which are tossed after one use. You no longer need those tools to mix or store custom colors.
Nail polish is a potential household hazardous waste because it's flammable and can contain toxins such as toluene and dibutyl phthalate. Because of this, some areas prohibit disposing of it with your regular trash.
Keep it and make something new.
Ever found a hard gel that you loved but it only came in a pot? The pottle gives you a choice in how you apply the gel you love. Use as a pot or bottle. Save money by buying in bulk to refill your pottle.
Sometimes we switch brands for budget or product testing. Keep your brand private in a pottle.