I beg to disagree. I've seen so many cases of people being rejected just because they made "minor" mistakes in their applications (including me): wrong NOC code, miscalculations of work hours, empty fields, missing documents.
I agree that all the info is always initially provided by the applicant, but showing it properly makes a big difference. I also agree that there's crooks and scammers, but you can't put all lawyers in one bag. Look for one with a proven record of approved cases, meet with a few of them before making a decision.
If this process doesn't mean much to you or can't afford it, then do it yourself. Otherwise, having a good lawyer can bring certainty, experience and context to the outcome. CIC has standards and expectations. There's always a certain degree of interpretation in their decision and lawyers can ensure that the right evidence is there.
I wouldn't risk a life changing process just to save a few bucks. Money can always be regained once in Canada.