The point of the needle is designed with the fibres of the fabric in mind. For example the leather needle has a chisel tip to penetrate the hard fabric. The ballpoint needle slides in between fabric fibres to prevent pulls.
It is also important to understand that needles come in different sizes. The size of your needle will depend on the type of fabric you are sewing, how thick the fabric is and the weight of the thread you are sewing with.
Janome have just launched the Purple Tip Needle to their range. These needles are designed to eliminate skipped stitches in stretch fabrics. The green sample fabric below was stitched with the Purple tip needles on the last two rows of stitching. It has made an enormous difference to the quality of the zig zag stitch.
It is recommended that you change your machine needle every 8 hours of sewing. You can usually tell if your needle is going blunt when you hear it popping into the fabric. Many sewers change their needle for every project. If in doubt, change it. The needle is the cheapest item to replace on your machine and amazingly enough will eliminate 50% of problems that occur when stitching.
So off you go and change your needle!