Symmetrical peaks with tailing factor of 1( this is the ideal tailing factor of course) results in accurate intergration of the peak area and also peak hight specailly in quantitative analysis. Check the formula in USP general section.

The most ideal peak resolution is aimed at As (asymmetry factor) of 1.0 where Tf is at 1.0 and resolution is ~2.0. The asymmetry factor change in the corresponding analysis to higher values deliberately lower down resolution since asymmetry factor is calculated at 10% of peak height and tailing factor is calculated at 5% of peak height as per USP. Any deviation from the normal distribution indicates non-ideality of the distribution and the migration process, therefore might jeopardize the integrity of the peak's integration, reducing the accuracy of the quantitation. But simultaneously, better chiral resolution will not only depend on these factors but also on selectivity factor (α), retention factor (k).

To get more clear idea you can visit this site:

http://www.forumsci.co.il/HPLC/WEB-Pharm_Review/HPLC_pharma_WEB_15-2-10.html