IIRC it gives a pretty significant advantage as most fencers are used to right hand opponents

Random stat I found on a site that doesn't cite a source :

While only 10% of the general population is left-handed, roughly 30% of Olympic fencing medalists have been left-handed.

Edit : Apparently it's not just about unfamiliarity, due to how fencing works:

However, the geometric differences in left-versus-right fencing mean the advantage can be narrowed but never fully eliminated