I have 2 of them and both are on beds. The first was really my self-training on different techniques, color placement and pattern design. The second is swap blocks with a bunch of my own added to it to make it king size. The common themes in the first quilt are blue & white stars. In the second it is black backgrounds with bright fabrics, mostly stars.
To make a sampler quilt more cohesive, stick with a theme or color. Like Eleanor Burns' Egg Money Quilts done in 30's repro's.
Why do you think they can't be used on a bed?