Question re: back of tank - keep glass clean or not?

[newreefer_59]

Attached is a pic taken Jan 1. The space between the wall and back of the tank is just enough to squuueeezze an arm back there to clean with my magfloat and Easy Scraper and is doable - though it is a pain. So, is it generally ok just to let coraline algae, etc to just grow on the back pane (or is it personal choice? As per pic, I did paint the back blue initially. I do get some (not alot) of short hair algae that my blennie munches on, but wondering if it is beneficial to just leave the back pane or should it be kept as clean as the front and side glass.

Thanks.