Other than saving money, one of the biggest reasons I shop online is the fact that there is a wider range of sizes available in the products I love. I have very small feet, US size 5.5, which is nearly impossible to find in most stores in North America, and if they do carry my size, they are usually sold out because they will only get a very limited number in stock. The great thing about shopping online is that they will carry uncommon sizes and have more in stock than in stores. You also have access to designers that specialize in making items in the size you need (in my case, these are European shoe designers that size smaller than usual.)
Whatever your size needs, you can bet that you can find it online and no longer have to face that awkward “we don’t carry that size here” conversation with salespeople.