It is easier — even quicker, once you have the habit — to say In my opinion it is not an unjustifiable assumption that than to say I think. If you use ready-made phrases, you not only don’t have to hunt about for the words; you also don’t have to bother with the rhythms of your sentences since these phrases are generally so arranged as to be more or less euphonious.
phrasesquotes
It is not enough for the phrases to be good, what you make with them ought to be good too.