It would depend on how many points you need overall.
The basic requirement is 67 points right now (subject to visa officer discretion). But extra points in some areas can supplement what you are missing in others. For instance, if you have a Master's Degree, or a spouse, or arranged employment, these could give you more points and allow you to have fewer points awarded from your IELTS exam.
You can get a free assessment from Campbell Cohen by following this link:
https://www.canadavisa.com/assess/canada-immigration-assessment-form.htmThis is correct; in my personal experience, I took the test almost 2 years ago and... Shame on me... I did not good, I got 5.5... so I guess as our friend thaiguy just said, it depends on the officer discretion and how many points do you have overall, I don't remember exactly but I think I had over 75 points on my initial assessment, bottom line I think it helped me a lot.
Cheers
Eduardo