Is it normal practice to disable passcode during repair?

Here's what Apple says about it:

Before you get service for your iPhone

Your content is important, and you’ll need the backup to restore your iPhone after service. Apple might delete the content on your iPhone during the service process, regardless of whether you bring it to your carrier, take it to an Apple Retail Store, or mail it in.

Before you bring in your iPhone, back it up
Before you send in your iPhone, follow these steps

If your iPhone has a SIM card, remove it and keep it along with your accessories and adapters—don’t send them in with your iPhone.

After you receive your replacement or repaired iPhone, transfer your SIM card back to the iPhone and turn it on. You can set it up as you would a new iPhone or restore your content from your backup.

copied from Service Answer Center - iPhone

Before you bring in your device

Follow these steps before you take your device to an Apple Store, Apple Authorized Service Provider, or carrier. If your device won't turn on or respond, finish as many steps as possible:

1. Back up your device.
2. Have your Apple ID password ready. For some repairs, you'll need your Apple ID password to erase your device and turn off Find My iPhone.
3. Bring your sales receipt if possible, in case your service requires proof of purchase.
4. Bring your device and any accessories that you need help with.
5. If you haven't already, call to check whether you need an appointment before you go to a service location. For example, schedule a Genius Bar reservation before you go to an Apple Store.

Before you send your device

Follow these steps before you send your device in for repair or replacement. If it won't turn on or respond, finish as many steps as possible:

1. Back up your device.
2. Tap Settings > Messages. Turn off iMessage.
3. Erase your device: Tap Settings > General > Reset > Erase All Content and Settings. If asked, enter your passcode and Apple ID password.
4. Make sure that Activation Lock is disabled.
5. Remove any SIM card, case, or screen protector from your device and keep your cable and charger.

Now your device is ready to send. If you've arranged a repair request, you should have received instructions for how to mail in your device. If you didn't get instructions or you haven't set up a repair request, contact Apple Support.

Freewinds wrote:

My iphone 6S's screen is cracked and I booked genius bar yesterday to arrange the repair.

The genius asked me to disable "find my iphone" for repair. I understand this point and do it.

Then, he asked me to disable passcode too. Is it normal??? As I don't want to re-install all apps again after repair so I didn't erase my iPhone, so I feel extremely unsafe for this practice.

This is perfectly normal. As whoever works on your phone may have to restart it multiple times, even force restart it, they can't be running out from the back every time to have you enter a passcode. It would be even less safe to write down your passcode and give it to them. While there may be some less than honorable folks even working for Apple, it's quite likely that they would lose their job if they were caught looking through customer data, making it probably not worth the risk. Not to mention that they are incredibly busy.

The last time I took my phone in for service, I restored it to new ahead of time myself, in part because I was hoping the restore might solve the problem.

Freewinds wrote:

My iphone 6S's screen is cracked and I booked genius bar yesterday to arrange the repair.

The genius asked me to disable "find my iphone" for repair. I understand this point and do it.

Then, he asked me to disable passcode too. Is it normal??? As I don't want to re-install all apps again after repair so I didn't erase my iPhone, so I feel extremely unsafe for this practice.

Anyone has similar experience?

Thanks

When right there in the store, yes I've had that asked of me. The reason being that they can then check function without simply wiping the device and reinstalling iOS (in which case you would have to restore from backup at home to get all your content back). The tech in the back can replace the display and then immediately check basic function before they bring it back out to you. Remember the genius who greets you out front is rarely the actual hardware repair tech - the genius is just going to hand your phone to the Apple certified repair tech who actually replaces the display.

Of course, if it failed basic function checks they would have to wipe it and reinstall iOS so you should always still have an up to date backup at home.