LVM (logical volume management) is a technique that is independent of file systems. However, as a volume resizes, the underlying file system must be resized as well. In other words, LVM is nearly pointless when used for file systems that cannot be resized.
For file systems that can be resized, the ability to be resized online is important. This means that a script can run periodically to see if a volume is nearly full. If so, the script can extend the volume size using LVM, and resize the file system on-the-fly. There is no incurred down time as far as services are concerned!
Some file systems can be extended on-the-fly, but not shrunk on the fly. This should pose little practical concern because in a practical server environment, a file system typically only grows in size.