I have one because it has a 'special' meaning to me that no-one else would get.
During the Falklands war in 1982 I was serving in HMS Valiant and the nuclear submarines involved were referred to in low security signals etc by a simple 'code' that related to the order in which all the SSNs were built, regardless of whether they were to be involved in the war or not, ie:
A1 HMS Dreadnought
A2 HMS Valiant
A3 HMS Warspite
A4 HMS Churchill
A5 HMS Conqueror
etc, etc
On return and getting ashore, I happened to see that the personalised plates A1 DLH and A2 DLH were available from DVLA for £600 and £300 respectively. As A2 was the code for my boat and it was followed by my initials I opted for that one and still have it on one of my cars.