No need to leave it on always ... it's a filter that gives a certain effect, use it when you want this effect.
Polarizing filters stop polarized light from entering a camera lens. By filtering out this light, a polarizing filter eliminates reflections and haze from your photos. It also increases the contrast and depth of color of objects, such as the sky or foliage.
The downside when you use a polarizing filter is that it cuts out the equivalent of around 2 f-stops of light. This means you’d need to compensate for 2 f-stops of light exposure with this filter on your lens. This perhaps not a good thing when you're taking low light photos or want to freeze motion.
A polarizer can also be problematic when filming as the effect varies with the angle to the sun ... making the effect come & go when you turn. Also not good to use for panoramas for the same reason.