This is just my own humble opinion, but when it comes to using a few extra KBs here or there, here is my penny's worth. A Website customer generally has the following expectations:

• Good Google Listing
• Good looking
• Good performance - speed wise and navigational wise
• Uniqueness
• Good price ...

Appart from the third point, nothing is affected by using a module like jQuery or Zepto. Nowadays though, 9 out of 10 times a possible performance improvement of not using jQuery is not really noticed by the viewer. What speaks for using it is: dependance of other handy modules needed, code readability (team work, shorter code), speed of development.

The same goes for using other usefull tools like grunt (grunt-postcss, etc.) ...