[1] Usually this is because the captain thinks their team has already scored enough runs to win the match and does not wish to consume any further time batting which would make it easier for the opponents to play out for a draw.
[4] Frank May proposed at the Annual General Meeting of the Marylebone Cricket Club on 2 May 1906 that in a two-day match, the captain of the batting side has power to declare their innings closed at any time, but such declaration may not be made on the first day later than one hour and forty minutes before the hour of drawing stumps.
The existence of the follow-on law makes amassing a very large lead worthwhile as it can prevent the game from being lost due to how long it would take a team to equalise the scores even if they avoid being bowled out.
A significant amount of the highest innings totals in Test cricket have come from the team batting second and some have gone on to win those games.
[6] As recorded in The Ashes' Strangest Moments, as the pitch at the Gabba began to dry, England declared their first innings at just 68/7, in order to exploit the conditions.
"[7] A team batting in the 3rd innings of the match can declare in order to attempt to bowl out their opponents in a short amount of time rather than allowing the game to meander to a draw.
In their 1984 tour of Sri Lanka, New Zealand beat the hosts by declaring to set a target of 263 runs shortly after lunch on day 5.
Arjuna Ranatunga scored 51 but the rest of the team collapsed around him and shortly after his caught & bowled exit off John Bracewell it was Stephen Boock who took the final wicket with Sri Lanka on 97 from 28 overs.
The fact that a team ends their innings and gives up the chance to score mores runs can make declarations a bad decision in hindsight.
In the 2nd Test of the 2012–13 Border–Gavaskar Trophy the Australian side declared so they could bowl at India for 3 overs at the end of the first day rather than see if their final pair of batsmen could score additional runs.
Jack Crapp hit 10 runs off 3 balls to secure the win which came one minute before the 4 day game was due to finish.
In August 2020, in a rain-affected match between Durham and Leicestershire in the 2020 Bob Willis Trophy, both teams agreed to forfeit an innings in an attempt to produce a result.