Highly degraded samples tend not to be amplified evenly across the genome. In general, an average fragment size of 2 kb in a DNA sample is the lower limit, assuming no portions of the genome are degraded to the point where information will be missing. Often, when the largest fragment in a gDNA sample is 2 kb, other fragments are much smaller and some regions of the genome may have been lost due to degradation. At least a small portion of 10 kb fragments or larger need to be present in the gDNA sample for even amplification of the entire genome.
Note: If you are interested in amplifying DNA from paraffin-embedded samples we recommend to use the REPLI-g FFPE Kit.