The truth is that Americans probably need more—not less—vacation time.

While many workers in Finland, Brazil, Russia, the U.K., and France are entitled to as many as 28 to 30 days of government-mandated vacation a year, there are no government mandates in the United States, and full-time workers (with 5-10 years of tenure) typically receive about 15 days, according to Mercer’s Worldwide Benefit and Employment Guidelines report. Add in national holidays, and many workers overseas get about 41 vacation or holiday days each year, while Americans get 25—just above Canadians’ 19 days and Chinese workers’ 21.

Experts say that it’s critical to refresh yourself. So go ahead and schedule the vacation and take a chunk of time, not just a couple of days here and there. People don’t seem to really relax until the second week.

But keep in mind that there are occasionally some viable reasons to stay in the office and postpone the vacation for a bit. Here are five instances when a vacation may be the wrong call:

When the company is in crisis. Leaders and key players who face chronic, long-term business troubles will eventually need time off to decompress, but shorter-term crises require immediate decision-making. If a company’s survival and solvency is at stake, you don’t want your leaders or key players taking off for a leisurely vacation. You’ll also be seen as a get-things-done problem solver and indispensible team member if you weather the storm and play a part in the organization’s turnaround.

When you’re in the middle of a project. Employees need to predict and pay attention to important deadlines well ahead of time. Whether it’s a group project coming to fruition, a major presentation, or a product debut, you definitely want to be there when it’s going to be unrolled, revealed, or when they’re going to be presenting it. You want to be visible and considered a key contributor to the project when the important news is being broadcast.

When it’s the busy season for your company. Many businesses are cyclical like accounting firms, landscaping contractors, wedding planners—and employees should take the seasonal fluctuations into account when planning trips. You want to be sure you’re giving your group and your supervisors the impression that you have the company’s best interests in mind—you are there and you’re doing what you can to drive revenue. There are additional benefits to being in the office during the busy season and taking your vacation later. If you take a vacation during the busiest days, you’ll most likely face more interruptions, so it’s to your advantage to take your vacation at a slower time.

Immediately following a merger or acquisition or during key client visits. Visibility is critical in the period following a merger or acquisition, as your company and team are being scrutinized for things like relevance, productivity, and necessity. One of the chief concerns after a merger is staff redundancy, but showing up and working hard can help employees make a case for themselves and their jobs. Another point when visibility is critical is when a person of authority is traveling to your branch or office. You want to be there to maintain your identity as a strong player. Many of these visits are scheduled in advance, so the onus is on the employee to plan for them.

Anytime a key team member or supervisor leaves. This is the ultimate opportunity for you to step up, take on a leadership role, and set yourself apart as it’s all about creating value in today’s workforce. Employees have to position themselves as that star athlete, performer, and player. Offering to take over some responsibilities can increase your marketability and branding prowess at work.