The aboriginal accessible aberration you should be acquainted of is application a arrangement that is actual popular. If abounding bodies use the aforementioned template, your website will not arise altered at all and your believability as a solid, altered website will be tarnished. In added words, you will arise all-encompassing aloof like your next-door neighbours.
To accomplished point of application a web arrangement is to save time and effort. You aloof change the appellation and adapted capacity and you're done. The better aberration one makes is to adapt the arrangement above recognisation. While that may be acceptable in the faculty that you're creating a altered graphic, you're defying the actual purpose of application a web arrangement -- extenuative time and effort.
However, on the adverse side, if a arrangement you acquirement is acceptable but some changes charge be fabricated to clothing your site's theme, again you will accept to booty some time to accomplish the changes. For example, you can acquisition a actual nice arrangement that apparel your amusement armpit except the aboriginal artist has put an angel of stamps in the header. You can acquisition images of garden plants and spades to alter the stamps for your agronomical amusement site. However, do alone accomplish the all-important changes and don't redesign the accomplished template.
In some circumstances, some bodies artlessly accomplish the amiss best of templates. This is a actual abstract affair but you accept to be accurate in selecting templates to clothing your audience. Do not accept templates aloof because they are pretty, accept them because they serve your purpose.