It depends on the target genome. Usualy, specific primers for DNA fragment PCR amplification ranged from 16 to 25 nucleotides. 10 nuceotides will give non-specific amplification due to low Ta. They will set on many non-target sequences in the studied genome.
primers about 10 nt lenght are used for RAPDs, AFLPs and you definitely don't need shorter primers, because 10 nt is enough to get just reasonable amount of fragments for polymorphism analysis, but you must be careful with the reaction conditions - a little change in protocol will give you different result as 10 nt is not specific enough.
here's a revised AFLP protocol of improved reproducibility: