Primary elections are the elections conducted by political parties to select the candidate for the main election. In US, the main political parties select the presidential candidate by primary elections only. In India, there is only one party which conducts primary elections to select the candidates.
When I came to know about it, I liked the idea, and thought that, all parties should do in big scale. Recently, I came to know that, there are many drawbacks to this for small parties.
To win in an election, generally the candidates do not require more than 15-20% of total votes. Average polling percentage is 60%, and if anyone gets 30% out of the polling votes, most probably they will win. With many parties participating in elections, if there is tough competition, people can easily win with 20% of the polled votes. It means, if 12% of voters vote for that person, they can win. Even otherwise also, if 20% of the voters vote for them, they are going to win.
If there is a party which can influence other parties fate, then other parties also would become active in the primary elections of this party. Let's take there is a party A which wants to conduct primary elections. Party B would lose, if a good candidate from party A contests. So, party B wants the weakest candidate of party A to contest in the main elections. If there are primary elections, then party B would help the weakest candidate in all the possible ways to win in the primary elections. In India, in the main elections itself, most of the people take money and vote. For primary elections, it would be very easy. They can go to slum areas, and if they give Rs.10, they will vote for whichever candidate they want. By this way, parties which have more money can influence the candidates selected by another small parties. If other parties can influence the selection of the candidates, there is nothing more suicidal than that.
However, if all the candidates in the primary election are equally strong in most of the dimensions, then there may not be any disadvantage. But, if atleast one weak candidate contests in the primary elections, then other parties will try to influence the winner and the party which conducts primary elections is at loss.