Yes, it often does matter, for example if the project is a restoration project. Couple of reasons:
First, plants have ranges within which they grow “naturally” or as native to the area. Some plant species have very wide ranges, others very narrow. Many good guidebooks to native plants provide thumbnail maps showing the range for a plant. Especially with plants with wide ranges the species may be adapted to local conditions of temperature, precipitation, etc. This could be true across a local area as well, for example where a species may be more tolerant of marine salt near the coast, less tolerant inland. So for a restoration project you might want to collect seed locally, grow it out, and plant from that for good results.
Another reason is that plants live in plant communities, meaning you might find certain plants typically growing together in “natural” conditions. Some ecological areas are even named for their plant communities. For example: the maple-beech forest in northeast USA and lower Canadian shield. Plants growing in communities may just have overlapping ranges, or they may have some kind of symbiotic relationship. Using plants grown from local seed could help get the best of such relationships.
Here is an interesting US NPS article on working with native plants: http://www.nps.gov/plants/restore/pubs/intronatplant/planning.htm
