If the end use of the pcr product is proof of existence of that amplimer, sequencing template ,size of repeat sequences and many other aspects of pcr then I do not think that the final extension makes any measurable difference. For TA cloning it may improve the proportion of A overhang product in which case the extension should be done at the optimum temperature for the polymerase used

I got this information from Thermofisher and I think it may help you. "Final extension evaluation

The final extension step follows the completion of the last PCR cycle. In this step, the PCR mixture is incubated at the extension temperature (generally 72°C) for a final 5–15 minute period. The duration of this final step also depends on the amplicon length and composition and should be optimized to ensure full-length polymerization and good yield of the target DNA. In addition to filling in incomplete ends, DNA polymerases with terminal deoxynucleotide transferase activity (TdT) such as Taq DNA polymerase add extra nucleotides to the 3′ ends of the PCR products in this step. Thus, if a PCR amplicon is to be cloned into TA vectors, the final extension step of 30 minutes is recommended to ensure proper 3′-dA tailing and efficient PCR cloning (learn more about TA cloning)"

I totally agree with Mr. Bashiru answer