Shall we travel together? No thanks!

A friend who is making plans to go to Iceland in summer, upon hearing that I have also been considering the Scandinavian island as a destination for a summer trip, suggested that we travel together if our schedule does match.

It is nice that someone considers you as a possible travel companion, but I am not sure that it will necessarily work just because we are friends.

There are obvious advantages in travelling with friends. Co-planning not only makes preparation easier but is also part of the fun. The costs can be lowered through sharing resources and splitting accommodation and transport expenses. Above all, having the company of friends makes the journey less lonesome and much safer.
However, both from what I have heard and personally experienced, I know that this business of travelling with friends can be very tricky. If not handled well, the trip can turn into a disaster and in extreme cases may ruin a friendship. Let's face it, it's easy for friends who only have a meal or a drink together once or twice a week to stay on good terms, but for them to have to live together for a length of time is an entirely different story. When you have to make lots of big and small choices and decisions on a daily basis, many different factors come into play. So before travelling together, you have better be sure that you and your friend know each other well enough that (1) there won't be any personality clash, (2) you have similar views, interests and preferences about a lot of things, and (3) your enthusiasm and conversation topics won't run dry after the brief initial spell.
Unfortunately, such trips do not always end as well as they start. Some people have to part company with their travel partners midway because of some differences they cannot resolves. Some people may have finished the trip together but with the friendship seriously dented. A former travel companion of mine said it well: "If friends can go on another trip together, it speaks volume about their friendship." This travel companion and I have not considered doing another trip although we never had any disputes or grudges during the only journey we had together, so there you go.
The saying that familiarity breeds contempt is very wise indeed.