Source: p 287, Sweet Reason: A Field Guide to Modern Logic (2010 2 ed) by Henle, Garfield, Tymoczko.
[1.] Predicate is the reason we started on deductions. In Sentential, remember, we can verify that an argument is valid by using truth tables or the short-cut method. With Predicate, we have no such tool. We can show that an argument is invalid if we exhibit a universe in which the premises are true and the conclusion is false, but (until now) we have had no means of showing that an argument in Predicate is valid.
In the 2 Logic textbooks read (the above and Hurley's), each exercise on deductions (e.g. the following) divulges the conclusion of an argument (whether or not valid). But without computers, for a given collection of > 10 long convoluted premises: What if the conclusion were concealed or tacit? How can you determine it yourself?
I am assuming that you must at least conjecture the conclusion, before attempting (dis)proof?