Using /execute if entity @e or /execute unless entity @e without "run" subcommands (which is a replacement for testfor commands) no longer gives off an output relative to result and will be successful in command blocks regardless of result.
Has the same issue for /execute if:unless block
Commands such as /data get no longer have the practical output of "result" using comparators.
Commands such as /scoreboard players get no longer have the practical output of "result" using comparators.
Additionally, using comparators with things like /difficulty and /scoreboard players get no longer gives an output of "result", which was useful with doing complex calculations and computing using command blocks and comparators.