From a conversation with an Asthma Nurse it seems to be the case that many on Oral Steroids including prednisolone (but other oral steroids too) see an increase in appetite. This can often result in weight gain.
As 'higher weigh' can contribute to increased inflammation (and as Asthma is a condition considered to be caused - at least in part - by inflammation) Asthmatics can well do without an increase in their appetite / weight.
Having an awareness that your appetite may well increase while using oral steroids is important (especially for those who are already over-weight) as it may help some to be more self-disciplined when in the vincinity of the Biscuit Tin.