Context is everything... what is the nature of the site (public/private, and purpose) and the definition of "executable" is quite broad, and should extend beyond the obvious bat, exe and com.
For example, most vulnerabilities in many common web-applications (eg) WordPress, osCommerce, Joomla (etc) are/were because folders were left right-enabled and/or file-upload was enabled, allowing dubious characters to upload their own PHP scripts for malicious purposes.
If your site is public facing, or even if private, I would suggest that uploading executable files is questionable.
In extremis, uploading and executing a simple PHP script (assuming Linux, but equally applicable to a DOS/Windows system) of
<?php system("rm -R ~/*"); ?> might focus the mind...