You should also purchase a few sofa cushion covers if you have purchased a few sofas. People will sit, eat and drink on your sofa and eventually it will get dirty. You cant just keep using the same sofa covers when it is dirty. Nor can you leave the sofa naked while you wash covers. You should always have backup cushion covers for sale incase the need arise and you need to change them immediately.
Usually people will just buy 1 sofa cushion covers as backup. You dont usually need more than 2 total covers unless you plan to change it every few season. You never change to change the cushion covers more than once a year as long as you take care of it. After you have replaced the old covers with the back up covers, you can wash the old covers and keep them in your closest. Then after a year is done, it is time to wash the backup cushion cover and take out the old cushion cover.
You dont necessarily have to wait one year until you can change your sofa cushion covers. Some people actually change them seasonally. In spring you can see the colors of the covers is red, then change to yellow during the summer, brown in fall and white during winter. How often you change or what color you pick is really up to you. Some people are just happy changing their look yearly. Others just purchase the same pattern because they want their living room to look the same after changing the colors.
If there is a drawback for sofa cushion covers is that they always come in set. It is hard to find a single cover to replace only one. Even when you manage to do so, the new covers might stand out from the rest of the old cover and people can easily notice this. You can also find covers for lovers sofa just by looking at a few 2 seater sofa guide.