To reconcile the joining of two pieces of fabric when one is larger, or would prefer to take up more space than the other.
1. Dealing with uneven pattern repeats
There are times when the pattern repeat of a print or weave is not exactly the same at one end of length of fabric as it is at the other. Over a long length, say 50 metres, the variation can be quite problematic. Or the fabric might have been cut form two different batches- especially if bought as and end-of-roll or sale piece.
So there is need to make the longer pattern repeat fit the shorter one, without ruckle or creasing. Shrinkage is the first and often successful option, whatever the cloth. By steaming just the selvedge of the whole piece it can often be made to fit – certainly within a few mm.
Repeats that are far out may be shrunk if the material is wool, the problem is that when one side has been shrunk and the other not, there might be laundering issue down the road. So, as always the situation decides.
b) Often in couture and dressmaking, less so in home furnishings, there is need to ease one fabric to another in order to create a form – such as the fit of sleeve to armhole. In furnishings it might be a circular ruffle to a lampshade hem, an insert, godet or any one martial to a fixed band. In this case any excess material is eased in place using pins and as many of them as is needed to take up the fulness invisibly…..
see pinning / basic techniques