Some people use primer to see where flaws are still in the model that they may have missed such as filling gaps, scratches, etc. while others use primer to aid in adhesion of the final color on the model.
Many of us here, myself included, don't use it very often as we see no need in it.
If you are painting it with enamels and have prepped the surface well then paint adhesion should not be a problem, but with some acrylics you may or may not have adhesion problems if you need to mask over it.
Whether or not you want to use primer is up to you.
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon