It's not so much advantage, but the fact that in some situations "single-sided" won't work.
"Single· and "Double" sided is not necessarily down to chips on one side or another - but the type of chips and the addressing schema.
The important thing with RAM is reputable design, construction and chip quality. There are 3 grades of RAM, generally speaking.
Grade 1 is full specification chips from a branded manufacturer, on JDEC specified boards, built and fully tested by a major brand name.
Grade 2 may use good quality parts, but not built be a known brand name. They may not be tested to full margins, may use lower than JDEC quality boards.
Grade 3 (sometimes called OEM grade) may have chips that failed full margin tests - very unlikely to be on full spec boards (may have less smoothing/decoupling capacitors) and assembled by who knows.