Does it make sense for different opposition groups to field one candidate in the two-round system?

Question

Does it make sense for different opposition groups to field one candidate in the two-round system, including in non-democratic countries? I don't see the point. Each candidate has their own voters, including "unique" voters who won't vote for a "single" candidate or whatever the English term is. The more people turn out for an election, the less there's a chance the ruling party or the incumbent gets re-elected in a first round. And a runoff, whoever the opposition candidate is, has a mobilizing effect for voters who do not support the authorities (including ones who didn't vote in the first round because they didn't believe the change was possible). I've been reading one book about Belarus, here's one passage (this particular one is about the 2001 presidential election).

Вик и подхватил предложенную политтехнологами от оппозиции идею выделить среди бесчисленных кандидатов основную группу, куда вошли Михаил Чигирь, генерал-полковник Павел Козловский, Семен Домаш, Владимир Гончарик и лидер коммунистов Сергей Калякин.

Отчасти создание «пятерки», как эту группу сразу стали называть в прессе, было разумно. Так появился хоть какой-то шанс уменьшить количество кандидатов, не раздирая голоса избирателей. Если эти пятеро сумеют договориться между собой, может быть, и другие последуют их примеру, и в конце концов Лукашенко будет противопоставлен единый кандидат от всех оппозиционных сил.

my translation:

Wieck <this Wieck, an OSCE representative> was the one who took up the idea suggested by the opposition's political strategists to pick out from countless candidates a key group that comprised [a list of names].

In a way, the creation of "the five", as the group was now called in the press, was reasonable. It gave at least some chance to shrink the number of candidates without tearing the constituents' votes apart. If those five are able to come to an agreement with each other, perhaps, others will follow suit, and eventually, Lukashenko will be challenged by a single candidate from all opposition forces.

(from here)

What "tearing the constituents' votes apart" is the author talking about? Doesn't coming up with a "single" candidate meet that description, if anything (since "unique" voters won't show up at the polls)?

Answer 1

One possible motivation to "pre-unify" to a minimal list of opposition parties is that campaigning during the first round necessarily involves anti-government hopefuls campaigning against each other.

After a long nasty first round campaign of oppositionW calling oppositionL's reputation and competence into question, oppositionL voters, assuming oppositionW went on to the second round, may not feel all that good about voting in their previous rivals. So squabbling within the opposition to some extent profits the government who is guaranteed to move to the second round anyway.

This is somewhat related to what happened in the USA 2016 and 2020 elections, where disgruntled Sanders voters might have cost Hillary the election in the first and where Sanders, to his credit, ensured his best it would not happen to Biden in the second.