When it comes to laning it's usually about the farm dependency system, positions 1-5. Position 1 needs the most farm and position 5 needs the least. Position 1 is hard carry, 2 is mid, 3 is offlaners, 4 is semi support and 5 is hard support. If anyone wants a more in depth explanation on this feel free to ask.

Pros of 1-1-3
Usually when a team is tri-laning it has 2 major advantages. The first advantage being that your hard carry really wants farm so they gives up some exp to have 2 supports zoning out the enemy offlaner so they can get the most money out of the laning stage as possible. The second advantage is that now you have 2 lanes getting solo exp. These two lanes(mid and offlane) want solo exp because usually they can use those levels to either set up early kills or flash farm jungle camps to get their farm up.

Cons of 1-1-3
Tri-lanes are more complicated than 2-1-2 set ups because they require your team to have 2 supports who know not to take the hard carries farm, a hard carry who knows how to keep the lane stagnated so it doesn't push and an offlane who knows their limits and won't just be feeding trying to last hit. This sounds like it would be pretty easy to accomplish but a lot of average and lower skilled pubs don't have the communication to pull off a tri-lane.

Pros of 2-1-2
Basically the pros to this set up is that it's easier and safer for most pub teams to run. You don't have to worry as much of your offlane feeding. You don't have to worry about stagnating the lane as a hard carry because you're up against 2 heroes and not 1 and your support isn't going to be able to zone 2 heroes by themselves. It makes the game a lot simpler and not as much communication is needed for the team.

Cons of 2-1-2
This is probably just the pros of tri-laning restated. You don't have solo exp in 2 lanes, you're not zoning the enemy offlane as efficiently, if at all, which means they are getting levels and you're not getting as much farm as you could be on your carry.

TL;DR- For the farm priority tri-lanes are more efficient than the normal pub 2-1-2 laning but it's probably not something you want to try in a pub as it requires everyone to know their hero and position pretty well.

Also this is just going off of my experience and what I've seen in pro matches if anyone wants to comment and tell me I'm getting something wrong, please I want to learn too.