HOW CAN I TIME TRAVEL?
This depends on your device specifically, and some don't have the capacity to do it. It involves changing your time settings to enable extra gifting and energy restoration. There are some good existing threads explaining the specifics of how to time travel and issues you may come across. Use the search box to find these.

PROS
You can basically have unlimited energy and strength and send unlimited gifts.

CONS
You can affect other things on your device such as alarms or reminders and other apps. You may experience more crashes and have issues with your device after travelling.

SHOULD I TIME TRAVEL
A completely individual choice! Just make sure you read the previous threads about it, and go in to it with your eyes wide open! Also see "Backing Up Your Game".