change job scope

i'm changing my job scope..currently i am supporting sales, marketing & project.. however starting from 1dec, i will be supporting marketing only..i will be doing 4 exhibitions instead of 1 exhibition.. reason for change?? my colleague tendered her resignation..n my boss wants to keep her.. so we have this change.. dunno whether gd or bad.. cos i still do not know which field i wan to go into specifically.. but all my colleagues say that moving into sth specific like marketing is a gd step for my career path.. hope it really is a gd move..but my workload is thrice as much and there is no pay increment..sob sob..