Living Materials - is like a wooden table that is still alive. The purpose of living materials is that they are self sustaining and maintaining. using the ambient environment. One particular set of living material is Living Sealant for underground habitats or for reactive Atmospheres.
Living Sealants are organisms are designed to grow around walls to reinforce them and to feed off ambient waste and heat. Many worlds prior to colonization or habitation have gene-gineered living building materials. The advantage is that it brings down complexity by removing some tasks from life-support.
If one starts accounting for all the tasks than need to happen to keep a fully enclosed ecosystem going, its better to having some complex tasks automated through making biological tools perform it.
Other living materials, are plants or what are organism that recombine common elements into a more usable form for colonists. They could grow like runners along the floor of a harsh world, usable as fibers, they can grow up or down into the planet usable has building materials of various qualities (strong and light, dense and insulating).
There are times the seeds are not growing fast enough, a disaster or fate can always cut supplies short and sometimes there can be an oversupply. Gene-gineers can use technology to zero-out a genetic template for their own uses.
Livestock is another form of biotechnology. Livestock creates chemical-cocktails like milk, fuel, glue, etc... (which some Living materials can also provide) using ambient chemicals of the given environment. They care for themselves, and are sometimes designed to perform a human-useful task (like burrowing tunnels or building structures for human habitation).
Another valuable use is a source of Labor and Transportation, require no other infrastructure or ecology except what it is designed to survive and accomodate. Sometimes they can become a source of food, when infra does not allow Hydroponics and Protein Vats.
What is important is Gravity to Hold an atmosphere, Heat, and a variety of ambient reactive elements that an engineer can build a life-form out of.
The variety is limited to only the imagination and ingenuity of the engineer. If technology allows living creatures built out the spewing elements of a start, if the TL is high enough some engineer would probably try to build an organism that feed off that and accumulate the energy and elements.