Are HV/HP switchable pumps as capable as a specific HP or HV pump? There are generally two big specialties for pumps. High Pressure (HP) or High Volume (HV). I ride Fat bikes, mountain bikes and road bikes, so I'm confused about buying a new pump to carry while on rides and whether I could find one pump to rule them all?

I know there are good pumps that do high pressure and others that do high volume. However, there are several that claim to be switchable between HP or HV.

How effective is this? 

Will it be as effective as a dedicated HV pump on my fat bike tires? Will it also be able to put 110 lbs of pressure in my road bike tires as efficiently as a HP pump? Or are these a compromise that kind of works, but less than a purpose made HV or HP pump?

Examples of switchable pumps:
Giant Control Mini Combo Pump
Blackburn Mammoth Mini Pump
Raleigh RMJ604 2 Stage Switchable Pump
Answer: No.  Any tool intended for a specific job will always be better at that specific job than a multi-purpose tool.

That said, pricing may mean that a single pump is sufficient for your needs.

Fat bike tyres have a lot of volume to fill, but generally they don't go to high pressures - I'd be surprised if you're running them at anything above 40 psi.

Note I assume you're not talking about shock pumps when you say high pressure - they are used on higher end shock dampers and not tyres/tires.

You said "less work" but from a wording point of view, the work remains the same, your input multiplied by the efficiency of the pump will approach the total work required but never equal it.  So a 50% efficient pump will feel like you're doing more work than a 75% efficient pump.