The reason why political parties create platforms is to make sure that they’ll be able to provide policies that are consistent to the principles and ideologies of the party. Voters would have an idea of how the government would go about in dealing with different issues that the country has such as problems in health care, education, foreign policy, welfare.
Political Parties create platforms to inform their voter base/voters in general of the party's stance on certain major issues, which may be turning point.
e.g. The √-1 Party is Pro-Choice, wants 100 Weeks of Maternity/Paternity Leave, loves gun rights and thinks toothbrushing should be mandatory.