Private Acts were so named as they passed powers or benefits to individuals or bodies rather than the general public. Parliament's role was to arbitrate between the promoters of these Private Acts and those affected by their projects, as well as to take account of the public interest.
Such Acts might be needed if a communal right of passage was being taken over. For example, when turnpiking a road, or when land needed to be purchased and a joint stock company created to raise capital - as when building a new railway.
Parliament's Private Bill procedure was unmatched in any other country and it had major advantages. Local transport needs could be brought before the national legislature and a legislative tool provided, thus enabling the collection of tolls or the compulsory acquisition of lands.
It also had disadvantages. A contested Bill could be extremely expensive. In an extreme case - such as the Great Northern Railway Bill of 1845-46 - the promoters alone spent £433,000.
Decisions could also be inconsistent. And while local interests might be accurately assessed, the national interest tended to be neglected. Attempts were made to remedy this, for example by requiring railway Bill committees to consider a report on the proposal from the Board of Trade.