Molecular biology labs often house multiple -80 C freezers and liquid nitrogen tanks. I can think of only one function for which these are absolutely required: storage of mammalian cells and cell lines. Indeed I have never tried to store eukaryotic cells in a regular (-20 C) freezer, but I doubt it would work well. However, -80 C freezers are often used for storage of all sorts of other stuff, such as bacterial stocks, proteins, RNA, etc. For these items, would there be any serious problem with storage at warmer temperatures? Sure, there might be a small increase in rate of degradation, but for a “basement” molecular biology lab setup, I doubt the huge cost associated with an ultra low-temp freezer would be worth it. I’d stick with a good, cheap -20 C freezer.