Just check the hp (requirements of the implement). Older small square bailers can run with minimal power. Round bailers, on the other hand, especially anything over 4x4 and net wrappers require serious power. Newer small square bailers also require power. Example, my 575NH high capacity square bailer requires 75 PTO input for maximum production. That's not to say that you can't run with less but in heavy windrows, it requires more power. A 575 would really load your engine and possible cause damage.
Other problem is if you bale squares with a wagon on the bailer, you need a tractor with enough weight to safely pull the bailer and wagon plus the flunkies loading the wagon. A 4000 pound tractor pulling a 3500 pound bailer plus a 4000 pound almost loaded hay rack is asking for big trouble, especially on hilly ground.
You don't pull a tandem axle equipment trailer with a Volkswagen Jetta. It's all about common sense and safety.