You have
two types of point scales for immigration to Canada. First you need to be deemed eligible, and if you are, you'll be attributed CRS points once in the Express Entry pool.
1/Eligibility points, which mean you need to have at least
67 out of 100 to be eligible for FSW program and enter the Express Entry pool. These points are attributed based on different factors
(education, language, etc...) called
"The Six Selection Factors". More information here:
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/express-entry/eligibility/federal-skilled-workers/six-selection-factors-federal-skilled-workers.html
2/CRS points, which rank you against all other eligible candidates in the pool, and based on which you'll receive an ITA if your score is higher than the cut-off for the given round of invitations.
Each of these two point scales systems have different point distribution criteria. To stay in the topic of work experience here as an example,
the maximum work experience points one can get in his CRS score is for 3 years or more.
However,
for eligibility points, the maximum points you can get is not for 3 years, but
6 years or more.
What that means in practice, and to answer your initial question again:
--> With 3 years of experience, you get maximum CRS points, but miss out on potential eligibility points which max out at 6 years. So if you're comfortably sitting at or above 67/100 eligibility points, and therefore don't need the extra eligibility points for work experience, then you can settle with just 3 years of work experience. But if you're short on eligibility points, it's better to show proof of work experience for more years.
