It's not a matter of truthfulness.
Actually it is.
It may be a gin clear day, but for those of use stuck in a radar room don't know what it's like outside, and really have only the hourly metar to go on (or the guy who has just come in from having a smoke and says "Hey, it's clearing up out there" or "You should see the cell down to the south west".) It also removes any doubt, as I have had an instance where matey boy called up at 40 miles with "I'm a PA31 blah blah blah, inbound to land" who had filed VFR but was IMC and didn't say anything until told to "Maintain 3000 VFR at all times"................ Uhhhhhhhhh.