Bike tire liners are an additional layer of protection between your tube and tire that can help prevent flats. They are especially useful if you are riding in an area with a lot of glass or other sharp objects that could puncture your tire. Liners also provide a bit of cushioning to help absorb impact and make your ride more comfortable. Some riders find that they need to use less air in their tires when using liners, which can also help prevent flats.
Whether or not you need bike tire liners depends on the type of riding you do and the conditions of the roads or trails you ride on. If you frequently ride on rough terrain or in areas with a lot of debris, then liners can definitely be helpful in preventing flats. If you mostly stick to smooth pavement, then you might not need them as much but they could still be beneficial. Ultimately, it’s up to you to decide whether or not bike tire liners are necessary for your rides.