Unlocking the bootloader - what do you lose?

1) I would like to know if I'll unlock the bootloader, is there any drawback?
E.g.: in Sony phones the DRM keys are lost forever without any backup.
2) Is there any way to lock it back?
3) Can the stock recovery be used to install other roms/ packs that are renamed to update.zip?

Many thanks in advance!

Sent from my Le X820 using XDA Free mobile app

Dell Venue 3840 HSPA+ lose mobile signal

Hi guys, so I just got a dell venue3840 hspa+ yesterday for my mother. But after I change sim card, the tablet totally lose mobile signal and I tried many ways I found by the internet.

Cause I lose it by change the sim card, I don't think it is the hardware problem.

Today I will try to flash dell stock rom hopefully can get mobile signal back.

If you have any suggestion please help me, the wifi work well but sometimes I need the 3g outside