I scrape the back & sides. I do it weekly right before a W/C. Already doing maintenance, so why not! Don't take long if I do it once per week. Usually just get a few calcium specs. Occasionally, if I let it go two weeks, I begin to see some Coraline spots, but they come right off.
I have a :deep see blue" back ground, so obviously, specs of Coraline look terrible.
I did let it grow on the "black" back wall of my Biocube. It is only used as a quarantine tank anyway. Hard to scrap that plastic background so I left it!