Trouble is allowed for it's benefits because it sure has benefits that accompany it.
Why does God allow troubles for his children? Well, there are many reasons that can be best summed up in one word:benefits.
Tests and trials strengthen and shape our characters, makes us better persons and better Christians.
Sometimes, it could be that God trust us and want to boast of to Satan or want to see how you will handle the situation before He takes you to a greater or higher height of blessings. The case of Job in the scriptures is a very big example of the above statement starting from when God asked Satan if he has considered His servant Job, this question God asked was because He has trust where Job is.
The good news is that after all the tests and trials Job passed through, he over came, made God proud and was elevated as the scriptures recorded in Job 42:10-12 that "his later end was better than his beginning ......".
When God fashions His children for their place in His kingdom, He doesn't put them in lush lowlards, but high on rugged mountain sides where they must learn to withstand the storms of life. Those who endure become strong and sturdy.
The tests and trials of life also make us more aware of our own weaknesses and inabilities, so we learn to depend more on God and hold onto God for our dear life just like the tree on the mountainside that sinks its roots deep into the crevices between the rocks.
God proves to us that He is enough to sustain us in those difficult situations.
All these and many more are the reasons why God allows troubles.