直接加法(1+1)与SUM聚合函数的差异及性能准确性疑问

我想搞清楚直接加法（比如1 + 1）和聚合函数SUM(1 + 1)之间的区别。另外，我写了一段计算用户声誉值的SQL语句，采用直接加法组合多个聚合结果，想确认这种写法会不会有性能问题，或者导致计算结果出错——目前测试负值情况结果正常，但还是担心有遗漏场景。

以下是我用直接加法实现的查询语句：

SELECT
    "User"."id",
    "User"."name",
    "User"."title",
    "User"."about",
    "User"."location",
    "User"."isModerator",
    "User"."createdAt",
    (
--      问题投票得分
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NULL), 0)::int 
        +
--      回答投票得分
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
--      被采纳回答得分
        (COALESCE(COUNT("answer"."id"), 0)::int * 15)
    ) as reputation
FROM "User"
LEFT JOIN "Post" ON "Post"."authorId" = "User"."id"
LEFT JOIN "PostVote" ON "PostVote"."postId" = "Post"."id"
LEFT JOIN "Post" as answer ON "Post"."acceptedAnswerId" = "answer"."id"
GROUP BY "User"."id"
ORDER BY reputation DESC, id

我之所以这么写，是因为SUM函数不能嵌套使用——原本我想写成下面这种形式，但显然不可行：

-- ...
    SUM(
--      问题投票得分
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NULL), 0)::int 
        +
--      回答投票得分
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
--      被采纳回答得分
        (COALESCE(COUNT("answer"."id"), 0)::int * 15)
    ) as reputation
-- ...

我知道可以用嵌套查询来实现外层SUM，但觉得这种写法太繁琐，所以想确认当前直接加法的写法是否可靠，有没有潜在问题？

内容的提问来源于stack exchange，提问作者R.M. Reza