This option is being given by the Canadian government to those applicants who have genuine reasons for not taking their spouse along with them or not applying with their spouse for the PR visa. But this is used as a score pusher by many of the aspirants because a married person applying alone gets more points than a married person applying with the spouse. This particular option is used by many aspirants to increase their score which leads to an increase in their chances of getting an Invitation from the Canadian Govt. But these aspirants does not consider in to account the type of scrutiny done by the Canadian government after the issuance of an invitation to such an applicant.
There are very few reasons which are accepted by the Canadian government supported by a lot of your own government documents and an NOC from your spouse. If the Canadian government senses that you opted for this just to increase your score or if the Canadian government does not believes the documents you have submitted in support, then your application might get rejected. And just to give you an idea almost 50% of such applications are rejected every year. Even if you get the visa and you land in Canada, then inviting your spouse on a spousal visa or on a visitor visa is almost impossible and when you do it, the government senses that you applied alone just to increase your points and now your are inviting your spouse.