EliteFTS just came out with an article on board presses, should answer all your questions.
Also make sure ur doin them right... for example im weak 3/4 of the way at lockout.. it tells me i have to do paused 3 board presses with a closer grip. i do them as my assistance lift on DE and after a week i noticed it helped..
Board presses are used to improve lock out strength which is especially important if you use lifting gear. OR if you have a sticking point past half way. You should do board press starting with a narrower grip then working into your normal grip within the work out. You can also adapt board pressing to close grip bench work to kill the tris as you will not flare the elbows. It really helped me improve my bench in the last few months.
Look for something called 'Triceps Death'. I do that every few weeks and it is absolutely killer.
65-70% of their 1RM in the barbell bench press.
"We don’t have any set rules regarding when/how we perform “triceps death”. But, I guess the three most common times we perform “triceps death” are the following:
We will use “triceps death” as our main exercise on Repetition Upper Body Day. We usually perform 2 sets when using it in this manner.
We will perform 1 or 2 sets of “triceps death” after our max-effort movement on ME Upper Body Day.
We will perform 1 or 2 sets of “triceps death” after our dynamic movement on DE Upper Body Day.
The most common way we perform “triceps death” is by performing 5 reps off of a 1-board, 2-board, 3-board and 4-board (for a total of 20 reps)."