Weights must always be connected to a rig by a clip or link and never tied directly onto the line. This is because the top of a weight is liable to scrape along the seabed when being reeled in over a sandy seabed, or knock and catch against rocks when fishing over rougher ground. If the weight is tied directly to the line the knot will take all of this damage and become weakened and potentially fail during a cast with obvious safety implications. However, if a link is used then this will absorb the damage and the knot will remain in perfect condition.
As well as being an important safety feature links and clips also offer quick and fast ways of attaching a weight to a rig, and also allow weights to be easily changed during a fishing session. Links come in many different types and styles with teardrop shaped links being amongst the most popular.