Honking--- Getting out of the saddle and putting in a lot of pedal effort that causes the bike to go side to side. On a solo with rigid forks you will put in a lot of effort that will not make the bike go faster for long. With suspension on a solo or a tandem, the effort will be wasted as it is taken up by the up and down movement on the forks. On a rigid Tandem, it is bebatable whether the effort is worthwhile, due to Frame flex, drag on the tyres and amount of energy used.
We do get out of the saddle to get that little bit of extra pedal effort to get over a hill, but we do try to keep the Tandem in as straight a line as possible, without sideways movement. Still not convinced it works though.