An unaddressed benefit of going VFR-on-top is the ability to file a flight plan beyond navaid limitations. ATC can issue the clearance, and not worry about distance criteria.
An example would be a flight requesting
KBFF..KFSD at FL090. Before GNSS and ADSB, I'd give you three choices for such a route:
KBFF.V169.RAP.V26.PIR..FSD..KFSD. (Adds 75 miles to the flight)
- A climb to FL130 for radar coverage. (Aircraft may not be capable, long term)
- An explanation that you could go direct if you requested VFR-on-top.
Without explaining ALL of the options, I would not say anything about VFR-on-top, because I cannot solicit it. If the options are explained, it is not considered solicitation.
Also, some issues in the above answers need to be addressed.
"The VFR on top clearance is often given with a block of altitudes. Such as this from the reference document "Maintain VFR-on-top at or between six thousand and one zero thousand.” With this clearance the pilot can fly any altitude they want within this block of altitudes without having to contact ATC for further clearance."
This excerpt is from the instructions for holding separation, and should not be used in a clearance with enroute flight. That's because the pilot is responsible for separation from other aircraft. The ability to climb/descend to any appropriate VFR cruising altitude is inherent in the VFR-on-top clearance.
Lastly, as fjch1997 pointed out, being cleared VFR on top doesn't automatically allow you to deviate from your route.
"When an aircraft has been cleared to maintain “VFR‐on‐top,” the pilot is responsible to fly at an appropriate VFR altitude, comply with VFR visibility and distance from cloud criteria, and to be vigilant so as to see and avoid other aircraft. The pilot is also responsible to comply with instrument flight rules applicable to the flight (e.g., adherence to ATC clearances)."