It is not necessary to always have mobile data turned on. It depends on individual preferences and needs. Turning off mobile data can help conserve battery life and reduce data usage if you are not actively using internet services. However, having mobile data turned on can be convenient for receiving notifications, emails, and accessing the internet on the go. Ultimately, it is up to the user to decide when to turn on or off mobile data based on their usage habits and preferences. **

The mobile phone may not be turning on properly due to a variety of reasons such as a drained battery, a software glitch, or hardware damage. If the phone only vibrates when turned on, it could indicate a problem with the display or internal components. It is recommended to try charging the phone, performing a hard reset, or seeking assistance from a professional technician to diagnose and fix the issue. **

I'm sorry, but as an AI text-based model, I do not have the ability to physically interact with devices or access real-time information. I recommend checking the mobile phone's settings, battery level, and any recent software updates to troubleshoot the issue. If the problem persists, contacting the manufacturer's customer support or visiting a certified technician may be necessary. **

A turned off mobile phone is not essentially invisible, as it can still be detected by certain technologies. For example, law enforcement agencies and intelligence services have the capability to track the location of a turned off phone through advanced surveillance methods. Additionally, if the phone has a removable battery, it may still emit a low-level signal that can be picked up by specialized equipment. Therefore, while a turned off phone may not be easily visible to the average person, it is not completely invisible to certain technologies. **

No, a turned off mobile phone cannot be located using traditional methods such as GPS tracking or network triangulation. When a mobile phone is turned off, it stops transmitting signals to cellular towers and cannot be located using these methods. However, some advanced tracking software or services may still be able to locate a turned off phone if it has a backup battery or if it is connected to a power source. **

When a mobile phone is turned on, the operating system boots up and the device initializes its hardware components. The screen lights up, displaying the lock screen or home screen. The phone connects to the mobile network or Wi-Fi, allowing users to make calls, send messages, and access the internet. Apps and notifications may also start running in the background, depending on the phone's settings. **

Yes, mobile data roaming needs to be turned on if you want to use your mobile data while traveling internationally or outside your home network. Data roaming allows your phone to connect to a different network in another country, enabling you to access the internet and use data-dependent services. However, it's important to be aware of potential additional charges for data usage while roaming, so it's recommended to check with your mobile carrier about roaming fees and options before traveling. **

It is generally recommended to turn off your mobile phone in certain situations, such as during important meetings, in theaters, or in places where it may cause disruption or distraction to others. Additionally, turning off your phone can help conserve battery life and reduce unnecessary exposure to electromagnetic radiation. However, in emergency situations or when you need to be reachable, it may be necessary to keep your phone on. Ultimately, the decision to turn off your mobile phone should be based on the specific circumstances and consideration for those around you. **