Takes me back to a VFR flight down the west coast of FL, USA.
I teach my students now, if there is a radar service available then USE IT!!!
In any case, back in '94 low hours PPL in a PA28 decides that, because the ATC controller sounds busy I won't climb to Class B airspace and request flight following (to all intents and purposes a RIS) but just bimble down the coast below CAS at 2,000'. Now I am not going to go down the 'ah ah ah' spooky road and don't ask me why but for no apparent reason I just felt this coincidental impulse to lean forward and look up, just to see a wide mouthed, white faced Cessna pilot just about to descend into my roof; one hard, diving turn to the right saw me miss the bloke by God knows how few feet. The bottom line is 'an inch or a mile, we still missed', however, for the sake of 1,000' and a single radio call that potentially disastrous scenario would have been avoided. My c*kc up!
Please, if the service is available then use it!
No, you may not always get what you ask for but you do stand a damn sight better chance with than without and if you don't ask you don't get.
Edited to emphasise the following post - RIS will help but Mk1 eyeball is a bloody brilliant tool and should never be underestimated or ignored and I would never wish to suggest for one second that a radar service under VFR should or would absolve any PIC of his 'see and avoid' responsibilities.