The benefit of a wider gap comes from its ability to start ignition process better.
In the past, I've used the analogy of trying to start a bonfire with a match, as opposed to a plumber's blow torch. (Probably only oldtimers remember those pump-up, kerosene fired rigs.)
In the first year of GM's HEI ignition system on prodution cars (c. 1974), the factory spec. for plug gap was .080". They later backed off to .060", as that large gap was eventually hard on the secondary ignition system (plug wires, dist. cap and rotor). As that secondary system aged, it broke down and allow the spark to jump to ground in various places, taking the path of least resistance.
Remember that the reason Detroit auto makers went to a high output ignition system was to be able to get the combustion flame front going in a very lean situation, and as a secondary reason, to help get closer to complete combustion. All this was driven by new, tougher smog laws that were imposed by the Feds.
Don't forget that using a larger plug gap may effectively lean your carb settings, and may or may not give you spark knock. There are lots of variables involved in this operation, so a guy needs to do the old "cut and try" method to optimize gap settings for his particular bike engine.
This is the round-about explanation of why wider gaps (usually) make more power: you can run a richer mixture and get it burned, thereby making a little bit more power. These wider gaps can also help give your engine better throttle response.
History lesson: Longer, fatter spark is the forte of magnetos. Until just a few years ago, all blown nitro drag cars used mags. Finally, Mallory changed their system over to an electronic one, using the "mags" as generators, which sent the juice to a "black box", where it got jacked out of sight by large capacitors and toroidal transformers, and then sent to the "standard" coils and thereafter to the spark plugs.
Electronic igntitions do have a higher energy spark, able to jump larger gaps, but, that spark is of shorter duration. To get a longer spark from this type, MSD developed an ignition box that would give multiple spark discharges all the time the engine is running.
This works great at lower rpms, but above about 3000 to 3500 rpms, there's not enough time to get off 3 distinct sparks and the engine "sees" just one, albeit fatter than the usual, electronic spark.
