Bacteria aquires restriction endonuclease by horizontal transfer. The result would be -
Any bacteria is protected against its own RE by a companion enzyme, site-specific DNA methylase, which methylates the restriction sites recognised by that particular RE. If any bacteria acquire new RE by horizontal transfer, this RE will cleave bacterial DNA and kill bacteria.
Bacteria can undergo mutation
Bacteria causes death of host DNA
Bacteria cannot survive because it lacks DNA methylase that protects the host DNA
It helps in DNA proof reading in bacteria