Buying yarn for a pattern

Most pattern list the approximate amount of yarn you need to complete the pattern. It best to buy one ball (skein ) than required. There are many reasons for this:
-as it is an approximation it could be short. Best to have too much than too little.
-buying too much will ensure that you have yarn to mend the item if required.
-buying too much gives you options (i.e. if you decided to knit longer sleeves or body)
-buying too much will help you when shopping for more of the yarn (you may be tempted to toss yarn bands...it's easier to keep spare balls.)
Happy knitting,
Leanne