You firstly, have to outweigh the advantages of a friendship and a relationship. For sure, some of us prefer friendship over a relationship or maybe vice versa.However, we need to understand why such a thing happen in the first place.
In a relationship you have certain standard requirements that have to be met, you have to look good for that special someone, pamper them and such. Pressure is certain in almost every single relationship. Now take a friendship for instance, you talk on the phone usually, you see each other when you can, you can forgive and forget easily without any hard conscience. Intimacy is not a necessity, it's an option depending on how close you are

For a friendship, you can widen or narrow it as and when you like. For instance, you go to a party and u widen ur circle of friends but narrowing of circle of friends is not recommended.
Then there's arguing. I think this is not a good idea in either case. However you may get away with it and work things out if you are just friends. If you are involved in a relationship, arguments can cause a great decline in communication and ultimately, the relationship.
Both friendships and relationships need communication. You have to be able to tell the other person how you feel when you feel it. Otherwise it all gets bottled up inside of you and it could end up making you burst. This is not a pretty sight. I feel it is easier to communicate something to your friend however. Now you should be able to talk with that special someone but friends are more honest. If you're involved, you try not to hurt the other person. This is where communication comes to be a big part of relationships.
Accountability cum Resposibility is also another factor especially in friendships, be accountable for your actions and reactions. In relationships, you have to be accountable for things you do together and also when you aren't together to stay focused and faithful to the other person you are involved with. Infidelity is a big NO NO!
You are supposed to have fun in a relationship but you need a basis first. Essentially you need a friendship, a good friendship as a base for a relationship. This way you'll know if you get along, your do's and don'ts and your pet peeves. You can't build a friendship from a relationship but you can build a relationship from a friendship.
