I'm always looking for ways to spruce up a cake without messing with piping bags and tips. To be honest, washing piping bags and tips, in the words of a certain 6-year-old I know, "isn't my gig", so I try to avoid it if I can. Using an offset spatula to make swirls and stripes can be just as pretty and can save a lot of time.
Lately, my favorite way to spruce up the sides of a cake is shown here. The trick is to have a nice thick layer of frosting at least 1/2 inch thick around the sides of the cake.
Decide which side of the cake will be the back before you begin and start each row at the back because you'll see that the last swirl is hard to finish without running into the first swirl just a little.
Then, holding a large offset spatula parallel to the working surface, begin the top row of swirls. Rock the rounded tip of the spatula into the frosting and then slide and rock the spatula backward, away from the indent you just made, while easing up on the pressure. The spatula does not lift from the icing completely until you have finished the entire row. Repeat the rocking and sliding until you have gone all the way around the cake. Starting at the back of the cake again, repeat the process for additional rows.
The cake you see here is a small 6" 4-layer cake and two rows were perfect. My typical 8-inch 3-layer cake will take three rows of swirls.
It's pretty, it's quick, and clean-up is a breeze!
If you want to get fancy, you can get out your piping bag and use this method of decorating to get a similar effect.