I myself don't use a mesh bag. I prefer the "naked" method. However seeds are one factor to try to keep short time, if at all, out of your wine. Seeds can inpart additional tannin in your wine. Especially if any are broken.
You want the must liquid to get fully thru the fruit so you don't want a bag that would constrict too much.
Probably large fruit could have a more spacious meshing.