Let me guess, you're trying to use the Calclassics Constellations.

Spark Advance is... literally what it means. A piston engine does not have the same spark timing for all the range of revs, and normally the distributor, in old cars, or the electronic spark control in newer ones man the appropriate spark timing at all revs.

Appropriate for the kind of engine and the use that one wants to make of it, of course. What do you seek out of an engine? Performance? Economy? Those are pretty conflicting needs that call for different spark timings, and in cars they usually are compromises tailored on the kind of car that engine is going to be mounted on and the kind of buyer of that car (sport cars will have their engines tuned in a more performance-seeking and fuel-economy rejecting way than the engine in a city car, to make an example).

In the Constellation from L-1049 forward it was possible for the engineer to control the advancing or retardation of the spark of all and each singular R-3350 with a certain precision (while in our simulated world we must make due with ONE switch and TWO different settings for all the engines at the same time) granted them sometimes by the use of oscilloscopes to obtain the best fuel efficient profile (usually it was the economy of usage that was sought after) out of the four engines.

...and the best thermal profile as well, as too advanced spark timings tended to make the engines run VERY hot.

Piston powered prop planes without spark plugs advancing control instead tended to be somewhat less fuel efficient in any kind of usage than those planes who instead could, and that was quite an issue in long haulers like the Connies and its contemporaries, like the various DC6, DC7, B367, B377 and so on.

Let it be clear that in REAL engines, toying around with spark advance can trash the engine(s) pretty fast, and in fact there are things even in simulated Connies you cannot do with the spark in advance without blowing the engines into kingdom come (they come with damage modules that are quite ready to cheerfully force you to feather one or more engines). Be careful.

That is in a nutshell. Fair weather and soft landings.