Android optimizing window

After every dirty flashing there is android optimizing which takes too much time and battery ,it is due to wiping dalvik cache but can we avoid it? Is it safe to avoid?

bootloop N910F at optimizing apps

Hello guys, im very new in here posting, ive been always a spectator..

i dont know if im breaking a rule but ive asked for help and no one helps me..

i ve an unbranded N910F live unit demo, and ive flashed all the 5.1.1 official roms out there and i always get a bootloop... and i really want to install it on my phone to fix the issues of sync and crashes when using facebook etc..

if this thread breaks a rule, please move it or close it please

any help would be great

Nexus 4 wont launch, optimizing apps

Hi.

Yesterday my Nexus 4 turn off and then turn on again, on screen after boot animation appeared a windows that says "Optimizing apps" so I wait till the end of the process but after that phone wont launch. I tried to launch him many times but each time was the same. So I just flash the ROM from here
https://developers.google.com/android/nexus/images
then launch a phone but he is stack on boot animation for 30 minutes and I turn it off, lock the bootloader and the "Optimizing apps" window appears and phone went to the state from beginning.

What can I do to repair it?