Hi madhubanti,
USB_CDC_VCOM_BM provides full CDC class support while dev_cdc_vcom_lite_bm is a lite version which can only provide basic CDC function.
For example, if we look into the code, the lite version uses USB_DeviceInit() to do USB device initialization. While non-lite version uses USB_DeviceClassInit().
If the MCU resources are limited for your application or user only needs to utilize basic CDC communication, we recommend lite version.
If you need stable data transportation, full USB CDC class support and the on-chip memory is sufficient, we recommend non lite version.
Jun Zhang