Should parentheses be used in sums of the form $\sum_{i=1}^k A_i+B_i+C_i$? Is it possible to write $\sum_{i=1}^k y_i\log p_i +(n_i-y_i)\log(1-p_i)+\log \binom{n_i}{y_i}$ as one mathematician said it is correct but another said that one should write $\sum_{i=1}^k\left ( y_i\log p_i +(n_i-y_i)\log(1-p_i)+\log \binom{n_i}{y_i} \right )$

If in doubt, add parentesis. The expression under the sum is too large in this case, so I'd add them to make clear what is being summed.
