Why a leader have visits to other countries, there is no definite answer. So I am just giving my perspective.
In a country external influences have as much importance as internal ones. Ultimately country needs cheap imports and favorable policies in other countries which can promote its export and access of market along with strategic alliances for the future war or stability. These things are called diplomatic wins in short. That is the prime reason when we say new government of Nepal or Bhutan should visit India first then china which gives the signal if new government wants to remain close to us at the cost of China or not.
Now we can see the similar analogy to PM visits to other countries. Future only can tell what the country has got with so many travels. As of now its only words like access to Australia Uranium, Canada Fual, UNSC seat etc etc...
