Anything with a motor will run differently, usually safely but not always.

Motor speed is 120*frequency/poles.

For example, a 4 pole hair dryer motor will run at 60Hz, the fan will run at around 1700-1750rpm instead of 1400-1450rpm.

For fans specifically, this can be a problem because fan load (torque) increases to the third power with respect to speed. This means that changing the frequency to 60Hz for a fan designed for 50Hz will run it at a significantly higher load which can make it run at a worse point of the torque curve where it is less efficient and ultimately overheat.

Some electronics have filters based on their designed operating frequency, so signals may get distorted by switching frequencies (notch filters on sensitive signal chain things like ECGs devices) though many are designed for both nowadays.

Things like electric blankets are just resistive loads so there would be little effect, but if they have very cheap electronics it is possible that the timer functions would be analog AC coupled so the timers might run fast or slow.

• heating elements don't care about frequency
• modern transformers (any laptop adapter, phone charger, ....) won't care about frequency because internally it convert AC to DC and then produce AC again in a much higher frequency.
• inductive loads (like motors, fans, microwave) do care about frequency. A fan that was designed to work @ 60Hz could burn out @ 50hz
• some ultra cheap low power chines devices (say a tiny bug zapper or dim LED) can rely on capacitive dropper can also be affected. so a device designed to run @ 50hz could burn out @ 60hz (opposite from inductive loads)

Generally, you won't ruin it. Modern stuff with switching power supplies like laptops handle the difference automatically. Old motor-driven devices like record players may speed up or slow down depending on their rating, and large AC induction motors, like washing machines, might heat up slightly.

From my experience, if the device is not designed to handle the frequency in question, it matters to some degree.

I tried using a 60Hz hair clipper in a 50Hz country, it ran but it was LOUD and vibrated harder is the easiest example I can explain in practical effects.

Most things are going to be weird, not work correctly, or fail prematurely if they aren't rated for the grid freq. You can buy devices that convert for you but they're heavy and expensive and electrically inefficient because they have to invert the power to DC and then back into an AC voltage with a different frequency.

On the more technical side, the things that care the most are definitely motors, and resistive loads less so but still yes.

60 > 50, your motor will spin about 17% slower, which can cause strange effects but also your current will increase so you get a lot of effects of stuff getting hot and breaking faster.

50 > 60 your motor will spin 20% faster which will mess a bunch of stuff up also. Might work for a bit ok but then you'll start losing bearings and so on.

For resistive loads like a light or heating element then it'll pull more or less current than it's used to, which is why another poster in the thread talked about an oven burning their food or something.

Also anything that uses the grid freq as a timer, which is most things with any kind of timer built in, will not time things correctly.

To answer your question: it's usually safer, better, and cheaper to buy new stuff that matches the grid frequency vs buying a frequency transformer but it depends on your specific situation.

Short vacation? You might be able to get away with sending it, but your stuff will have unexpected results, might be unsafe, and could break. Like, I would be very cautious of a curling iron or hair dryer, common stuff people travel with. Electric blankets NO, because fires. If it's a work trip just get the right stuff for where you're going or a transformer if you have a lot of expensive, specialized equipment.

Japan is split and has both 50 and 60hz grids. Modern products don't have any issues with this (voltage is 100v typically). In the older days, this was an issue for things with clocks and motors from what I understand, but I didn't move here u til the 2010s

Some time ago, I ran across a frequency converter product meant for professional barbers to use overseas hair clippers. Apparently they are designed to oscillate with the mains frequency, and tear themselves apart when run with the wrong frequency?

Transformers are a fixed ratio, they will convert 110->12v, or 240 to 25ish volts. So a 110v transformer on 240v will most likely fry its device.

The frequency mostly doesn't matter, but some old oven clocks used grid frequency to keep track of time, which was an issue recently: https://www.theguardian.com/world/2018/mar/08/european-clocks-lose-six-minutes-dispute-power-electricity-grid