I had mixed reactions when this happened. But after taking the time to think on this, this trade is a big win for the Raptors. Here are some reasons
Before, you are making forwards like Siakam, OG, and Barnes try to bang on the boards with these big man for rebounds all game, getting bumped due to all the size advantages, then playing all those mins, while still expecting them to give you a good enough game from start to finish on both ends of the floor? That's not easy at all. It's not like this team is getting blown out in their losses, they play well for a solid period of time, but they can't sustain for a long time, which results in losing gas at the end. During the last 18 games they are 10-8 with all 8 looses coming as a result of that fatigue which causes losing those close games. Now, none of these guys have to worry about banging with dudes 20 to 30 lbs on them for rebounds all game or contesting shots against those kinds of bigs with Poeltl here. This creates less fatigue for the star forwards to be able to their thing offensively while also giving more defensive energy to be able to close out these games better. It's not crazy to say that they would be 14-4 instead of 10-8 had they had a big like Poeltl.
The myth is the Raptors aren't a good offensive team, which isn't true they rank 11th in Offensive rating, its the defence which is worse at 17th. This move promotes the way the Raptors want to play defence. It's get in your face guarding up and make the ball handler as uncomfortable as possible. In the past, guards can blow by them and there is very less resistance on the help due to not having a big like that. Now while you might blow by them, there is resistance at the rim, and it becomes much tougher for the guard to turn that into a positive play. Like think about it. This team has an elite all defensive player in OG. Siakam, Barnes, and Precious are among the most versatile defenders in the league. VanVleet and Trent are always near the top in deflections. Yet they are currently 17th in defence. Why is that? No big man to provide resistance. A defensive big man is very important. You can have as many wing defenders as you want, but if your center can't defend, you won't be successful, the center is always the most important part of the defence. If you add that kind of defensive big man to the team, there is officially no holes, and it becomes a nightmare to score against the Raptors. That 17th ranked D is likely to rise to top 10 at worst.
Adding the pick and roll + Offence
The Raptors don't use the pick and roll too much, but maybe that's because they didn't have a big. Well now they do. Poeltl is an excellent screen setter and roller. Which adds another dynamic to this already 11th ranked offence. Makes life more easier for whoever is the ball handler with that space. Pull up threats like Siakam, Fred, and Gary would feast in these scenarios. Add in Poeltl's passing ability when the help were to come on certain rolls to the basket.
We could be looking at a team with potentially a top 10 offence and defence which not many teams are capable of. Which could mean the Raptors are not as far from being a true contender as we think.