It will depend on the brand and the color. (I usually use oils, so that's what I'm going to talk about here.)
I've experimented with the cheap Michaels and Hobby Lobby brands and some of those paints are UNWORKABLE. Other paints within the same line are okay. Also, Jerry's Artarama "Soho" brand can vary. The white is useless, same with ultramarine blue. But I found the black, earth red, cad yellow hue, prussian blue to be tolerable. Of course, my expectations were lowered when I used them.
Depending on the brand, I definitely notice a difference between student and artist grade, especially in the cadmium colors, ultramarine, permanent alizarin crimson, and some other more subtle tints. The earth colors, phthalo colors, prussian blues are cheap and potent pigments, so even a student grade brand can be okay.
For some reason, transparent red oxide often sucks in student grade brand. At least the ones I've tried!
Also, whites really should be a higher grade. Some of the student grade whites are pretty bad. Though...it can depend.
If you are on a budget and want a higher end student grade, Maimeri Classico is pretty good. Even their white! Be sure to get them online, otherwise they're just too expensive.
As for the quality of the paints, and how that affects the painting when you sell it? What matters is the lightfastness of the pigment. If it's lightfast, then it's fine. I've sold paintings made with student grade paint here and never worried, because the paints were lightfast.