I got a new (to me) fat bike just last week. Previous owner had put a stem riser and (I thought) very short stem. As soon as I got home I searched for and found a longer stem and swapped it out. When I say 'longer' I went from what was (I later discovered) the stock 60mm stem to a ridiculous 150mm 'fishing rod' from a previous lifetime. First ride I noticed I was stretched out more than ideal. THen I dove into the first trail I saw and discovered the real problem - the amount of movement at my hands way out on the end of that crazy long stem was so extreme that I was shoulder-checking every second tree that I thought I should be able to weave around without issue. Both my arms were absolutely coated with spruce sap by the time I got home, which soap and water does not wash off.
I put the 60mm stem back on and it felt a little cramped so I did a little do-se-do with the slightly longer stem with a bit of rise from another bike and LO! A med-short stem made the bike corner much more quickly than with the fishing rod. I may get a bar with a bit of rise and go back to the 60mm stem just to see how the manufacturer intended the bike to ride.
I tell this story because it is fresh in my mind and because it is a direct comparison of very long/short stem differences in terms of handling.
There are also other concerns like weight distribution and fit. Depending on the type of bike and type of riding you do, you might have to decide which of these concerns outweighs the other. For instance, on my touring bike I also have a 150mm stem, but the geometry of the bike means this doesn't make the bike too unwieldy, and since it primarily ridden on paved or hard surfaces, the F-R balance isn't crucial. The most important thing for that bike is that it fits my body well enough to spend hours per day without discomfort.