When brewing a double IPA do I have to put the hops in steeping bag or do I just toss toss them in. This question applies to both the boiling phase and when I have to dry hop later!
For both boil and fermenter additions, using a steeping bag:
If you want your transfers to be smooth, you need a plan for managing hop solids. Many brewers have plans that manage hop residues without putting hops in a bag. But unless you have such a plan, item 1 alone, should be enough to get you to use a bag. Number 2 can be easily compensated for. As for 3 & 4, you probably don't want bittering hops in your fermenter or chunks in your glass. If you've pulled the hops out (especially pellets), you might be inclined to transfer a little more volume (5), and not leave so much wort/beer behind. But you do need to buy nylon or many muslin bags (6).
This will depend on what kind of hops you're using and personal preference. Let's start with the boil:
In general, hops in a bag are going to give you less flavor/bitterness than the same quantity floating freely in the kettle. You can weight the bag, to mitigate this somewhat. (with, say, a stainless steel ball). I don't have numbers for this; I can only tell you "less."
When using pellet hops, I will typically just throw them in and let them dissolve. They'll eventually end up on the bottom of the fermentor. Some folks like to avoid as much of this material as possible, so they use bags.
If you are using whole leaf hops, I highly recommend using a bag in the boil. When I first used whole hops, I just tossed them into the kettle. This led to a variety of problems, including a plugged sight glass and plugged dip tube (which I cleared with a sanitized latex glove). They also soak up a surprising amount of wort. If I were to use them again, I would bag them and use a sanitized latex glove to squeeze some of the wort out of them.
As for dry hops:
I like to bag all dry hops, to aid in removal. Some people like to see whole hops floating at the top of the carboy. Again, you'll get less aroma when using a bag, so you may want to weight the bag or compensate by using extra hops.
I didn't address plug hops, both because I have no personal experience, and they tend to be less popular than other forms. I would expect them to behave similar to whole hops, but perhaps others can correct this assumption.