Depending on the size of the class and the TA situation, it may make sense for student emails to go to the instructor, the lead TA, the regular TAs, or nobody.
If you have a lead TA, it might make the most sense for them to receive emails. The lead TA generally has time to deal with administrative issues, and is also more aware of course-specific details than the WeBWorK TA. Depending on the volume of emails received and the other responsibilities of the lead TA, it might be appropriate for the lead TA to redirect emails asking for mathematical help to other course TAs.
For a small class (50 students or fewer), the volume of emails will generally be small enough that the instructor can answer all emails themself.
As an extreme measure, one can prevent students from using this button at all. Students will of course still be free to open their email programs and compose emails the old-fashioned way, but this will cut down on the volume of emails sent.
How to make WeBWorK send these emails to the chosen recipient