The main benefit of a PFC is being allowed to sell your product and for the customer to be able to use your product. That's a fairly big one. This requirement kicks in at a predefined power level.
Other than that it makes it easier to deal with universal input as others remarked and generally makes for a nicer operating profile as your power conversion is not pulsed. That's mainly relevant for higher power conversion, in other cases its really just added cost and complexity.
For inrush current you may want to consider a triac instead of a relay.
For background this kind of requirement originates with fluorescent lighting which is a nasty load for electric grid. Basically drawing lots of current to uncompensated inductive (or capacitive) load throws off the mains theta which more or less creates load for no benefit. For SMPS the deal is using the whole sine wave and not just the top n percent of it which also messes up the power grid
The power quality side of things is a bit more complex having to do with real and "imaginary" load but it comes down to power distribution no likey.