Even with multiple looms, I'm always finding myself without an empty loom or without the right sized empty loom for the piece I want to weave.
There isn't much you can do if you want to weave a big piece and only have a small loom available, but there are a couple of ways to weave a small piece on a large loom without wasting [much] warp.
Remember that each Mirrix Loom is adjustable in height, so you can make your loom shorter when making smaller pieces. But that only allows for a certain amount of adjustment.
The first, and easiest way to save warp is to simply weave multiple pieces on the same warp. After you finish one piece, advance your warp and start a new one, making sure to leave room between the pieces for finishing. This is great if you are patient and can wait to finish multiple pieces before finishing the first one. Me? I'm not always so patient.
This is where an Extra Warping Bar Kit comes in handy!
This kit allows you to put TWO warping bars on your loom, leaving a space in the back of the loom with no warp. Not only does this save warp if you are weaving a piece that is shorter than the length your loom can make, but it also comes in handy if you want to easily get your hand behind your warp threads or if you're weaving from the back and want to be able to see the front of your piece.