The typical advice when working a swatch is to focus on stitch gauge and almost ignore row gauge. Beware of this as changing needles sizes can sometimes affect row gauge more than stitch gauge. So perhaps an additional swatch or two is in order if your row gauge is way off.
If you are working simple shapes it's true you can just knit to the correct measurement as given in your pattern and you can ignore the row gauge. However there are many places that this simply does not work. I've often heard Knitters comment that they were working on something like the Swallowtail Shawl (pictured above), and had to knit extra repeats of one of the 3 pattern stitches to get the correct length. The shape of top down triangles also changes if the row gauge is off varying from a equilateral to an isosceles to a right angled triangle. Another place that row gauge is very important is in the popular top down raglans. The shape of the armhole and bust area is heavily affected by the stitch to row gauge. If you don't get that right there is no way that you will be knitting what the designer originally intended. It could be better or it could be worse depending on your individual body shape. The correct fit of set in sleeves and their proportion to the armhole will also be affected by a row gauge that changes the sleeve cap shape. Even if you have worked to the correct cap depth, the curve of the cap is determined by the cast offs and decreases so a row gauge discrepancy will change its overall shape.
The final place that row gauge is important is for the horizontal front bands of a cardigan. The stitch pickups are calculated on the length and row count of the front of the garment and since not every size is test knit this is typically done mathematically. Therefore if your row gauge doesn't match neither will the pickups.
Let me know - are you re-swatching when you get stitch gauge but not row gauge?