basic question about OSCCON and HS_OSC

this is probably a pretty dumb question, but i have gotten rusty on PBP
i have a design with the 16F819 chip and it was using INT OSC at 8MHz

now i have a 20MHz resonator

when i changed the DEFINE from
INTRC_OSC_NOCLKOUT
to
HS_OSC

it got me wondering what exactly happens with the OSCCON register ?
is it now ignored?
i looked at the data sheet and perhaps missed it but i could not see where it says anything about this the operations of the internal oscillator when an external xtal is used
(i did determine by other means that the chip is running at 20MHz)

is the int osc shut down or gated out entirely ?
do any of the OSCCON bits now matter ?

also with a 20MHz resonator (w/ internal caps) when i probe either pin with a scope it kills the oscillation, this is not hugely surprising but it got me wondering about whether for a resonator i should be using XT_OSC rather than HS_OSC
as far as i know the HS is not for speed per se but rather for a drive level more appropriate for a higher freq xtal

and lastly in the M16F81X.INC file i notice
EC_OSC
what is that ? i don't recall that one
thanks