You can use a template when you need to cut the same shape(s) many times.
Let me qualify that: if your pattern calls for squares, rectangles, equilateral triangles (60 degree), or right triangles (45 - 90 - 45 degree), then you don't need to use a template.
But if you are cutting odd shapes (say a hexagon or isosceles triangle), then you probably do want to use one.
You can purchase templates in many sizes and shapes (for example, see:
http://frommarti.com/index.shtml ). These templates are thick (like your cutting rulers). If you know that you will be making the same shape in more than one quilt, then these might be a good investment. These also allow you to cut several layers of fabric in one pass.
Also available is thin “cut it yourself” plastic. This may come with grid lines (to make defining the shape you want to cut easier). This product is ok, but if you are going to make your own templates, I prefer to use thin cardboard.
When I say "thin cardboard", I am talking about card stock, not the kind of cardboard you would get from a carton. For example, I use the "envelopes" that I get when I have my photos developed at Walgreen's. You can also "double" it (put two layers together) to make it a little thicker. If you do that, use double-stick tape to put 2 pieces together before you cut out the template shape.
Whether you use thin plastic or cardboard, make the template like this:
1. Draw the shape you want or use the paper template shape provided in your pattern.
2. If possible, make a photocopy!!
3. Cut out the paper template from the photocopy. Compare it to the original to make sure it is exactly the same size and shape.
4. Use double-stick tape to fix the paper template to the cardboard (or thin plastic) sheet.
5. Use your rotary cutter (you may want to use the small 18cm size) to cut out the template material.
6. Put a thin pencil line around all edges of the template to make its outline easier to see.
If you do make your own templates:
a) put double stick tape on the bottom to grip the fabric as you cut it. Add more tape as the
stickiness wears off.
b) Use your straight edge [ruler] on top of the template when you cut fabric! Use your finger to make sure that the edge of the ruler is lined up precisely with the edge of the template (not hanging over - which would make your cut fabric piece too big, and not covering the template completely - which would result in the template being trimmed!).
c) Check every so often that the template is not getting smaller! You do not want to start out making 4" octagons and end up 100 fabric pieces later with 3.5" octagons! Compare it to the original template shape. You can also check to see if the pencil outline has been cut off. If necessary, make a new template by repeating steps 2 - 6 above.
Pros and cons of purchased vs. home-made templates:
Can be reused...........Yes..................Yes, but why bother? Make a new one.
Disposable..................I doubt it................Yes
fabric shapes.............Yes..................Yes, if you work carefully
One last point about using templates:
Often, you will need to cut fabric pieces in a certain shape and then also cut pieces in its reverse. These types of shapes might be labeled (for example) "A" and "A-R", where the "R" stands for reverse. So "A" might be a triangle with its point on the right and "A-R" might be the same shape with its point on the left.
If the pattern on your fabric is the same on both sides (as in most batiks, which are dyed), then you can cut your templates when the fabric is folded. This would give you one "A" shape and one "A-R" shape in one cut. If the pattern is NOT the same on both sides (that is, if the pattern is printed only on the top), then you can NOT double (fold) the fabric. If you do, you will have to throw out the "reversed" piece.
Of course, you can always stack your fabric (folded or unfolded as appropriate) to get multiple pieces from one cut.