The advantage is that you can turn on the master power to the A/C
without exciting the alternator rotor (which is an additional 1-2 Amp
load). It is useful if you want to check/use a radio on the ground or
extend the electric flaps when you are not planning to immediately
start the engine. There may be other advantages, but I can't think of
them. I do use the feature.

I have an avionics master contactor/relay for the electronics stack
that I installed almost 30 years ago for which I got a one time GADO
approval. It automatically drops out each time the master is turned
off. On startup, I must manually re-engage the self latching relay
with a panel pushbutton after being done with the engine starter. The
radio etc knobs and switches are rarely touched.

Cessna in those years did have an auto-disconnect relay that dropped
out when the starter was engaged, but my engineering concern (real or
imaginary) was still starter-induced transient spikes getting thru the
relays' relative timing, vs the wear and tear of operating the
electronic stack controls each time I started it.

In hindsight it is probably much easier nowdays to install a manual
switch, but it requires pilot memory to use it. However, FWIW, I've
never had electronic problems in the airplane, except for some Narco
manufactured-in ones. I also have been fussy about maintaining the
stack cooling system.

Maybe I'm just keeping elephants away?