First let us put aside the misconception that you need a toner to shrink your pores or to remove cleanser residue. You cannot shrink a pore. You can clean out a pore which will bring it back to it's original size but you cannot shrink the pore. As for removing cleanser residue, that was true years ago when many cleansers were not water soluble. Today, if you rinse properly you should have removed all traces of your cleanser. The only exception to this is if you are using the Oil Cleansing Method.
So why do you need a toner? Let me start off by saying there is no one toner for everyone. Just like using the right cleanser and moisturizer for your skin type, the same is true for toners. A toner is the second step to give your skin what it needs to become healthy and balanced.
Most toners will provide extra hydration which is important no matter what your skin type is. In addition, many provide anti-inflammatory protection which is important in a variety of skin types such as acne, rosacea, and even aging skin. Some are more astringent which helps to balance an oily skin. However, you must be careful when choosing the correct toner, especially for oily skin. You never want to dry out your skin with a toner even if you have very oily skin.Stay away from any toner that contain SD alcohol, ethanol and isopropyl alcohol or acetone. Of course, there should be no artificial colors, fragrance or other synthetic ingredients.
Most toners can be used either as a mist or you can apply to a cotton pad and wipe your skin. I love to include hydrosols also known as flower waters in my formulations. They are distilled from plants, are pH balanced and smell lovely. Like essential oils, each has different properties that can improve the appearance of your skin. There is a hydrosol for every skin type. Do you use a toner?