Technically: less magnetic force gives you more sustain, but practically speaking it's probably too small of a difference to notice.[0]
The middle pickup in a Strat-style guitar is often "reverse wound, reverse polarity" which, when combined with one of the other pickups, provides some hum cancellation.
If the neck+middle or bridge+middle combo is in parallel (most are) you'll get a slightly more hollow/nasal tone compared to the neck or bridge pickup alone. The jargon for this is "quack" as in "it has a lot of quack".
If the combo is in series, that's essentially a traditional humbucker (albeit with the 2 coils spaced farther apart than usual). It'll be louder and have more midrange. 2 single coils wired in series like a humbucker can often be too mid-heavy and start to sound "muddy" or "lacking in definition". Real humbuckers can get away with using smaller magnets (ballpark: half the size of single coil magnets) and their close physical spacing means the signals going into each coil are nearly identical, so adding them in series just makes it louder, without making it "muddy".
Often, players who don't use the middle pickup will keep it there but use the height adjustment screws to lower it deep into the pickguard, farther away from the strings. In my opinion, the most practical benefit of this is your pick doesn't bump into it, but there are probably very subtle tonal effects going on.
[0]: Whenever you have "electric guitar" and "subtle difference" together, I demand blind testing before believing anyone else's claims. I trust my own ears, but I know myself well enough that my eyes will fool them.
The middle pickup in a Strat-style guitar is often "reverse wound, reverse polarity" which, when combined with one of the other pickups, provides some hum cancellation.
If the neck+middle or bridge+middle combo is in parallel (most are) you'll get a slightly more hollow/nasal tone compared to the neck or bridge pickup alone. The jargon for this is "quack" as in "it has a lot of quack".
If the combo is in series, that's essentially a traditional humbucker (albeit with the 2 coils spaced farther apart than usual). It'll be louder and have more midrange. 2 single coils wired in series like a humbucker can often be too mid-heavy and start to sound "muddy" or "lacking in definition". Real humbuckers can get away with using smaller magnets (ballpark: half the size of single coil magnets) and their close physical spacing means the signals going into each coil are nearly identical, so adding them in series just makes it louder, without making it "muddy".
Often, players who don't use the middle pickup will keep it there but use the height adjustment screws to lower it deep into the pickguard, farther away from the strings. In my opinion, the most practical benefit of this is your pick doesn't bump into it, but there are probably very subtle tonal effects going on.
[0]: Whenever you have "electric guitar" and "subtle difference" together, I demand blind testing before believing anyone else's claims. I trust my own ears, but I know myself well enough that my eyes will fool them.