Stretchers or Temples as they are often called help keep your weaving width true, the draw in consistent and protect the edge warp threads. They are widely used by Scandinavian Weavers on most warps but are considered vital for weaving linen or rugs. Toika Stretchers are exceptionally strong as they are made from steel. If you lose the pin covers or ever wear out the pins replacements are easily available and kept in stock.
Place the stretcher at the reed edge of your warp and set the width before you start weaving, you may need to weave a few centimetres of cloth so there is somewhere to attach the stretcher. Keep the stretcher close to the fell of the cloth. Remember to move the stretcher regularly so it stays close to the fell of the cloth. I have read both that you should leave the stretcher in place when you finish a weaving session and also that you should remove it at the end of a weaving session. The choice is yours. If you do the latter make a note of which hole you had used to set the width so if the stretcher is adjusted whilst removed from the cloth you will be sure it is put back at the correct width that was set when you started weaving..
Don't weave too close to your beater, it's always good practice to wind your weaving on regularly but if you forget the pins can scratch your beater!