My employer is applying for a Green Card for me, and my paralegal asked if I would like to go for credential evaluation of my educational record. How does that affect a green card application?
From @Chikkadu's link (which is rules for H-1 visas only),
There are a number of outside organizations which evaluate educational credentials to determine degree equivalency. Some organizations may also provide an opinion on the equivalency of experience to education. It is important that the adjudicator distinguish between these two types of evaluations. The latter type of evaluation carries little weight . Although USCIS does not specifically recognize or accredit any sources of evaluations, foreign educational degree evaluations can be of assistance if they are thorough, well documented and specific in reaching an equivalency determination. [emphasis in original]
So if the immigration status for which you're applying requires a particular level of education, it may help to include such an evaluation, but the adjudicator won't rely on it alone, and it may be sufficient to include the evidence and make the argument yourself.
For many types of Green Card you need to prove that you have an educational background that is the equivalent of a US type of degree. That is what the credential evaluation is usually for.