This phrase, one of the most commonly heard in the Japanese business world, conveys appreciative recognition of another person’s labors. It could be used, for example, to greet a colleague returning to the office from an excursion to a client’s factory in an outlying area; a more elaborate translation might be “Your hard work is appreciated.” The figurative intention is to assuage the other person’s fatigue and commend his exertions on the firm’s behalf. A similar expression is:
This one, however, is generally reserved for use by higher-ups addressing the people who serve under them and by older employees addressing their juniors. Strictly speaking, it would be a breach of etiquette for a younger employee or an underling to say gokurou sama deshita to a senior colleague or boss—the one to use is otsukare-sama deshita. In less formal circumstances, the final word is often dropped from these expressions, yielding the abbreviated forms.
The phrase otsukare-sama deshita is often employed as a form of farewell to a colleague or boss at the end of the work day. The following exchange between fellow employees features an everyday example of this sort of usage:
Osaki ni shitsurei itashimasu.
Pardon me, but I’m off.
Good work today.
This sort of comradely send-off can help alleviate the stiffness that dominates the atmosphere in some offices.
Grammatically speaking, otsukare-sama deshita is a past-tense phrase. The present-tense form, otsukare-sama desu, is also used, but under different conditions—when the work in question is ongoing. Let’s say a colleague, Mr. Horiguchi, is phoning in from outside the office (he’s about to call on the printing firm Dai-ichi Insatsu) to pick up his messages:
Horiguchi desu. Ima Dai-ichi Insatsu ni mukatte imasu ga, nani ka renraku wa haitte imasu ka.
This is Mr. Horiguchi. I’m on my way over to Dai-ichi Insatsu. Are there any messages for me?
Otsukare-sama desu. Shoushou omachi kudasai.
Good work. Just a moment, please. I’ll check.
– Source: A handbook of common Japanese phrases –