FFP will allow better use of the reticle with less chance for error so if you think you are going to use the reticle to range, call shots, or for holdovers then yes FFP is very beneficial. If not then there isn't nearly the advantage.
An FFP scope keeps the size ratio between the reticle and the target the same throughout the entire magnification range. This is where guys make the comment that the reticle is big. It is big because in comparison to a SFP scope it actually grows in size along with the target as you increase magnification whereas a SFP scope will keep the reticle the same size as the target grows bigger with increased magnification. It is important to point out however that if the reticle on an FFP scope is acceptable to perform a precise shot at lower powers then it will be exactly as precise at higher magnification as well because the ration stays exactly the same. This is where many non FFP users get off base. The reticle does grow thicker as the power magnification goes up but it does so in relation to the target that is also increasing in size so the amount of precision between the 2 is the same.
A reticle being too thick has more to do with the reticle line thickness than it does anything else. The early FFP scopes, and some of the current ones, were too thick for my liking. This was in part because the technology for fine etched reticles wasn't around yet or wasn't as perfected as it is today. Despite the rhetoric about FFP scopes being expensive just because they are cool looking and popular they do cost more to make primarily because of the reticle preciseness that must occur. FFP reticles are harder to produce than SFP. Today you can get very fine FFP reticles on par with SFP models, if that is a concern.
I use both but personally prefer an FFP scope for big game hunting. I use the reticle for quick shots out to 4-500 yards so with an FFP reticle I can take a quick shot at any power magnification and know that the stadia lines are calibrated correctly. With an SFP scope I would have to be on high power typically to have the reticle calibrated correctly. For closer shots this isn't always ideal nor is it ideal if you have the mag set low or medium or even if it got bumped and you need to get a quick shot off.
I also really like being able to call shots with my reticle and an FFP scope is better for this as well.
For the rest of things FFP and SFP pretty much blend together and they do the same things.
As far as the negatives to FFP. Some guys mention they like to have a bigger target in comparison to the reticle, so they can see more precisely where to place the reticle. I can't necessarily argue with that point however I do think that benefit is mostly mental. Like I mentioned above the preciseness or the ratio between the reticle thickness and the target stay the same so if you get the reticle thickness to your liking by buying the right scope the rest is moot IMO.
One other caveat. I typically shoot out to 1/2 mile or so on big game and practice out to 1000, 1200 yards at the most. If I was doing more ELR shooting I do think there would be more of a benefit to SFP scopes for the reason mentioned above. I still am not sure if I would choose SFP as there are some awfully nice thin lined FFP reticles out there now but it would definitely muddy the waters!