Without

Without LVM, a filesystem is created inside a partition. Because the filesystems are inside the partitions, you can use the name of the partition to mount it.

See this article : Linux - Adding storage without LVM

With

With LVM, a filesystem is created inside a logical volume, not in a partition. The partitions are used as physical volumes (pvdisplay), which are added to a volume group (vgdisplay), in which a logical volume can be created (lvdisplay). In the logical volume a filesystem is created. Because of this, only the logical volumes can be used to mount the filesystem.

LVM adds an abstraction layer between filesystems and partitions. This is extremely handy because it's easy to add a disk (which is made physical volume) to a volume group which makes space available, which can be added to any logical volume in the volume group. When that's done, the filesystem in the logical volume can be enlarged with resize2fs, even online. Without LVM, it's not possible or very hard at best to do that.

See this article: Linux - How to add storage to an OEL 5 update 4 Linux VMWare Machine