Suppose a public WebApp is hosted on an EXtra Small (XS) Azure Virtual Machine (VM). What benefits and/or performance problems might visitors experience if a Memory-Resident Virus Scanner is run on that VM?
they would experience a detriment to response time relative to your VM resources. Beyond that its a guess question. "Some detriment, what specifically is unknown without VM environment specifics"
Lousy albeit concise answer. If you would like a more concrete answer: avail us to more concrete server resource information :D
Good luck sir or madam ! :D