This is one step many knitters skip and sometimes serendipity awards them, but often it does not. Knitting a swatch is required to make sure the yarn and needle combination you are using gives the measurements required by the pattern. The pros and cons of knitting or not knitting a swatch can be listed simply by saying if you knit a swatch it takes additional time, but if you do not knit a swatch and your gauge is off and all the time you spent knitting may be wasted.
Gauge is simply the amount of stitches and rows knit per inch. If the gauge of a pattern is four stitches in an inch and the piece is supposed to be 36 inches wide, you should be knitting 144 stitches. To illustrate the point, say you are knitting 4 and 1/4 stitches per inch, but still knitting 144 stitches the measurement is 34 inches around not 36, depending on what you are knitting it may not matter. To further illustrate, what if your gauge is 3.5 stitches an inch, and you still have 144 stitches, your measurement is now 41 inches instead of 36 inches. Gauge matters. The other downside is that you may run out of yarn, a sweater that is supposed to be 36 inches around and a sweater that is now 41 inches around take different amounts of yarn. The only time gauge may not and I stress may not matter is when you are knitting an unfitted item, such as a blanket or scarf, but even then if your gauge is off the item shape will be off or you run the risk of running out of yarn.
To measure your gauge, knit a swatch, in the pattern stitch required, that is at least four inches by four inches. Hold the swatch down and count off the amount of stitches that are supposed to be in 2 inches and put a pin in the front of the first stitch and after the last stitch. Measure between the two pins, the measurement should be two inches. If your measurement is larger than two inches, your stitches are too large and you need to go down a needle size, if your measurement is less than two inches, your stitches are too small and you need to go up a needle size. This process must be repeated until you get the correct gauge.
A swatch is worth knitting if you want to achieve the results shown by the pattern or if you want a piece of fabric to put through the washer and dryer to see what happens. After you knit your swatch, you should run it through the washer and dryer, unless based on the label it is hand wash only. Do anything you normally would do with the finished garment. This is when you might decide the yarn you have chosen won’t work for item you chose it for.
Gauge isn’t important if you have lots of family, friends or are knitting for charity, then when you knit something the recipient is whoever it fits!

