Hi there... I'm a respiratory therapist who worked for years in an ER (now in an ICU) and it is a really good idea for you to know what your peak flow is when you are feeling good and at what point your Dr feels you should seek medical attention. It is a helpful tool to see how bad the exacerbation is, and we do it pre and post neb Rx's to see if you are opening up at all. You can give yourself nebs at home till a certain point, but you don't know what your O2 sats are... in the ER we can monitor that, give you supplemental O2, back to back nebs (in which case you should really be on a heart monitor because a lot of Albuterol can make you VERY tachycardic), IV steroids, and other diagnostic tests such as a chest X-ray etc. We can also intubate and manage you with mechanical ventilation if need be.
Maintenance meds have really come a long way in recent years (Advair has changed my mother's life) but if you are even questioning if you can manage your asthma at home, you should probably be seen. I just attended the wake of a former co-worker (yes, a respiratory therapist) who died at home because she was trying to treat herself and she died. It can happen, I've unfortunately seen it. Be on the safe side!