Since RAM disk is used for temporary files, there is no problem even if the data is lost when windows is shut down. Other than what is written in the manual, is there any difference between checking "Mount as Removable" and not checking? For example, different write speeds.
Making any disk 'Removable' essentially disables Windows file caching for that disk. The caching system is disabled to prevent data loss in case the disk is suddenly removed (e.g. a USB stick is pulled out). Without caching, reading and writing to a removable drive is a little slower than to a regular drive.
Due to this decrease in disk performance, we don't recommend ticking 'Mount as Removable' for RAM disks unless you have a reason for doing so.