We can use multi-mode optical fibers for telecommunication.
Effective usage is restricted to only small distances as compared to single mode fibers.
You can see a typical cross section of optical fiber cable below :
In case of multi-mode optical fibers,
we have diameter of core greater(50 - 100 microns) as compared to single-mode optical fibers.
Hence, What will happen is:
More Data can pass at given time
More space for reflections within core
Eventually signal quality gets reduced over distance in multi-mode optical fibers