You are correct in assuming that Partial Mash and All Grain are BIAB-compatible brewing methods.
I would say that if you are planning on doing Partial Mash, a bag would be recommended since you usually don't want to lauter the brew (maybe you do in some cases, but not any I have come into contact with). This means that having some specialty grains and extract you could probably use a hops bag or similar to steep the grains.
When performing an All Grain using BIAB there has been some talk that efficiency suffers, where some people feel they don't get out as much "sugars" as wanted from the grains; see post. As far as I have seen, efficiency has not suffered for me (and a lot of others) when using BIAB and have usually had an efficiency of 70+ %.
Another thing to consider when brewing BIAB is to consider the amount of water-loss. Depending on how long you are willing to let the grains drain (for instance letting them sit in a sieve over the kettle to drip) you will have different amounts of water-loss. As a rule of thumb I usually calculate that 0.9 liters/kg malt is absorbed from the brew (I am very impatient :)).