Robertson, who has repeatedly been ignored for his requests out of Toronto has found himself as the obvious man out. Even though he has put up a respectable 34 points in his young career; it's clear Toronto has other plans for the forward contingent.
Therefore, Toronto should find a way to gather some assets for the unsigned RFA, either by signing and trading him or find compensation elsewhere. Here's where the offer sheet scenario comes in; with Toronto only holding onto $1.25M in additional cap space, any team could field an offer north of $1.25M in order to secure his services.
The caveat here is that normally offer sheets are attached with draft pick compensation, however due to Robertson's unwillingness to play, and Toronto's lack of interest it could see them lose out on those picks. According to PuckPedia, the offseason RFA compensation allotment has been released and for a situation like Robertson, it could benefit him only.
With there being no pick compensation attached to any contract under $1.51M, any team could strongarm the Maple Leafs into dumping salary to match the extra $300K to keep a disgruntled winger and see if they can acquire something more; if not, then they decline the offer, lose a player AND compensation for it.