Moisturiser helps keep skin comfortable. Primer is an optional makeup-preparation product chosen for a finish or wear problem, such as a surface you want to look smoother or an area where foundation will not sit the way you like. The two jobs can overlap, but that does not mean you need both every morning.
If moisturiser, sunscreen and your base already work well together, you can stop there. A primer becomes worth considering when you can name the problem it is supposed to solve and see whether it actually helps.
Not every primer is a mattifying cream
Some primers aim for a smoother-looking surface, some emphasise glow and some have a tacky texture intended to help makeup grip. e.l.f. Power Grip Primer, for example, is positioned as a hydrating gel with a dewy finish, not a product designed to make every face look flat and powdery.
That variety matters when comparing it with moisturiser. A hydrating primer may add a comfortable feel, but the word hydrating does not prove it will replace the moisturiser that suits your skin. A smoothing primer may change the look of pores without permanently changing their size.
Choose by the specific purpose, not just by the category. If the finish you dislike is excessive shine, another glow-focused product may be an odd solution even if it has very enthusiastic reviews.
First make sure the base routine is comfortable
Foundation that catches on dry, uncomfortable skin is not always asking for a primer. Consider whether the cleanser, moisturiser and sunscreen already leave the skin feeling right before makeup.
The AAD's dry-skin guidance puts appropriate moisturising care at the centre of managing dryness. A makeup-prep product can change appearance, but it should not be used to keep covering a routine that leaves the skin persistently sore or tight.
Apply the products as directed and give the layers time to settle. Then use a thin amount of foundation. If the base looks heavy immediately, reduce the foundation before deciding that another product underneath must be missing.
Try primer only where you need it
You do not have to coat the entire face because the tube is called a face primer. If the main issue is how makeup sits around the nose, a small, targeted application within the product directions is easier to judge than another full layer everywhere.
Use the application method designed for the formula. A tacky gel may call for patting rather than rubbing, while another primer spreads differently. Do not apply the same technique to every product because their tubes look alike.
Keep sunscreen use consistent with its own instructions. A decorative primer does not become your complete sun-protection plan simply because another version of the category includes SPF.
When another layer makes things worse
If the combination rolls into little bits, becomes slippery or pulls the foundation into patches, adding more primer is unlikely to clarify the problem. Simplify the layers and change one thing at a time.
Do not diagnose compatibility only from whether the first ingredient is water or whether a silicone appears somewhere in the list. Those clues do not describe the behaviour of the complete formulas together. A small real application is more useful than buying a replacement based on a social-media compatibility rule.
Try your normal base without primer on one occasion, then use the primer as directed with the rest of the routine kept similar. Compare the area you wanted to improve after normal wear. You are looking for a visible, useful change, not an obligation to find a benefit because you bought the tube.
Is the extra step worth it?
A primer is worthwhile when it improves a specific part of the finish or wear enough to justify another application. It is less worthwhile if the routine already looks good or if the extra layer makes getting ready more complicated without a clear result.
My starting point would be comfortable skincare, appropriate sunscreen and a base applied in a manageable amount. Add primer when that setup needs a particular adjustment. Keep it only if the improvement is clear enough to make the extra step worthwhile.