Whenever you make wine whether from your own grapes, fruit or from a commercially made wine kit there is one ingredient that is always present and used--even if you do not purchase it. Yeast is a necessary component of every batch of wine and whether you purchase it or whether it comes with the kit or whether you just the natural yeasts that are present on your backyard fruit, everyone uses yeast.
Wine yeasts vary in numerous ways including the speed with which they ferment, how throughly they complete the fermentation, their ability to settle out of the wine after their job is complete (this is called flocculation), how much foam the yeast produces and how healthy the yeast is that you are using.
Wine kit manufacturers are especially concerned with the speed at which the yeast ferments (most manufacturers advertise 28 day kits, etc.). They also want the yeast to complete its job (by converting the appropriate amount of sugar in alcohol) because unfinished wine can be too sweet and be too low in alcohol content.
Flocculation is very important because the wine kit manufacturers want the wines produced by their kits to be aesthetically pleasing. The reason that low foam is important is that too much foam present during fermentation can cause what is called a "blowout". Foam can force the airlock right out of the fermenter.
The health of the yeast is important because this is key to the yeast being able to begin fermentation in pasteurized juice, juice concentrates or in the juice of your backyard fruit.
Each yeast adds its own particular traits to the wine. Should you change yeasts? We do not know! Unless we have made a particular wine using more than one type of yeast we will not know if one is better than the other. If you feel the need, experiment!