Here's my take on this. Until you reach a certain level of technical proficiency, inexpensive craft store paints will serve you every bit as well as pricier miniature-specific paints.
That said, there is a difference, and a reason for the price difference (and it's not *only* because GW wants to rip us off.) Even amongst the craft store brands, there's the ones that cost a dollar, the ones that cost $2, and ones that are 3 for a dollar. The craft brands tend to not grind their pigments as finely, and the paints' binders don't stretch as far. I can dilute a Vallejo paint or presumably a GW paint (full disclosure here, the only GW paints I still have in my collection are a few from back when Cote d'Arms was their supplier) far more than I can an inexpensive craft paint before it "breaks."
These two points lead to my general recommendation for people joining the hobby, which is to start off with the cheaper craft store paints, because a) it doesn't matter for the vast majority of newbies, and b) it drastically reduces the barrier to entry. Once you're at a level of proficiency where the cheap craft paints are inadequate to the new techniques you want to try (and you have to be brutally honest with yourself here whether you truly are at that level) and then make the switch.
My own paint stable includes a number of different ranges, all selected for what they bring to the table. I'm a big fan of Liquitex "fine artist paint" although I think they've renamed the exact line I like since I last bought some - they were soft body acrylics, not sure what they are now. Come in flip top pots and are more liquid than the stuff in the tubes(medium body). Also Golden Artist Fluid Acrylics (sometimes abbreviated as GAFA in online discussions). The rest of my stable is a mix of Vallejo Model/Game Color and P3 paints. I own a few of the old GW paints, but stopped buying them after they switched to those abominable bolter shell pots. The frequency with which they rework their line is a strong disincentive to go back to them in my opinion.