参考

以下のページを参考にさせていただきました。ありがとうございます。
ActiveRecordのjoinsとpreloadとincludesとeager_loadの違い
 【Rails】テーブル結合

データ構造

companiesテーブル

id	name
1	A社
2	B社

servicesテーブル

id	company_id	name
1	1	Aアプリ１
2	1	Aアプリ２
3	1	Aアプリ３
4	2	Bの野望

パターン１ all(pluckなし)

companies = Company.all
companies.each do |company|
    company.services
end

SELECT `companies`.* FROM `companies`
SELECT `services`.* FROM `services` WHERE `services`.`company_id` IN (1,2)

パターン2 : all

companies = Company.all
companies.each do |company|
    model.services.pluck(:name).join(',')
end

SELECT `companies`.* FROM `companies`
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 1
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 2

パターン3 : join

companies = Company.joins(:services)
companies.each do |company|
    model.services.pluck(:name).join(',')
end

SELECT `companies`.* FROM `companies` INNER JOIN `services` ON `services`.`company_id` = `companies`.`id`
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 1
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 1
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 1
SELECT `services`.`name` FROM `services` WHERE `services`.`company_id` = 2

パターン4 : preload

companies = Company.preload(:services)
companies.each do |company|
    model.services.pluck(:name).join(',')
end

SELECT `companies`.* FROM `companies`
SELECT `services`.* FROM `services` WHERE `services`.`company_id` IN (1,2)

パターン5 : includes

companies = Company.includes(:services)
companies.each do |company|
    model.services.pluck(:name).join(',')
end

SELECT `companies`.* FROM `companies`
SELECT `services`.* FROM `services` WHERE `services`.`company_id` IN (1,2)

パターン6 : eager_load

companies = Company.includes(:services)
companies.each do |company|
    model.services.pluck(:name).join(',')
end

SELECT **省略** FROM `companies` LEFT OUTER JOIN `services` ON `services`.`company_id` = `companies`.`id`