For those concerned, the positive side of the electoral pact between the UUP and DUP is clear. A single candidate supported by more than one party is likely to mobilise the supporters of both, and so will get more votes than each could alone.
If, as in the time of the Anglo-Irish Agreement, the goal is to demonstrate support for a single political issue, this can be highly effective.
But the negative side of such pacts is less often appreciated.
Moderate unionists will sometimes attract Catholic votes if they have a chance of defeating more hardline candidates, and the SDLP gets significant (though I think not decisive) support from Protestants in all three Westminster seats it currently holds.
A united unionist candidate, or a single nationalist, would find that cross-community outreach much more difficult to achieve.
In addition, for the junior party in such an arrangement, the impact of failing to fight an election can be internally corrosive. Once your voters have got out of the habit of voting for you, especially if it was on your instructions, it can be hard to cajole them back.
That's why it is interesting that the quid pro quo for the UUP standing down in North Belfast, the seat the DUP are most worried about losing, and East Belfast, the seat the DUP most want to gain, is a clear run in two superficially less impressive prospects.
The UUP will not win in Newry and Armagh, and Fermanagh/South Tyrone is a difficult lift despite 2010's wafer-thin margin.
But the pay-off may come in next year's Assembly election, where the UUP is not far off a second seat in either area.
From the DUP's perspective, risking two Assembly seats in a year's time may be a fair price to pay for improving their chances in two Westminster seats in May.