Warming up is often one of the most overlooked aspects of any training session. Running late or short on time? "I'll skip the warm up it'll be fine." Can be famous last words.
Making a habit of this can not only expose you to injury but will also be highly detrimental to your long term progress.
The best cure for any injury is prevention. And the warm up is the perfect place to add in all of your preventive/ rehab type exercises to both activate weak and troublesome muscles as well as ensure you actually get them done consistently.
Bodyweight exercises are great to get moving with. Squats, lunges, push ups, pull ups, single leg deadlifts, crawls, jumps, climbs. The goal should be to mimic some of the movements you have planned in the main part of the workout and prepare your body for action. By doing this you also ready your body to handle heavier loads, meaning you will be able to lift heavier weights, leading to better results.
Simply jumping straight into the main part of your workout means you will also miss out on a great opportunity to add to the overall volume of a training session. Think for example if you simply add 10 push ups to your warm up every day thats an extra 3650 push ups every year… Its the little things that add up to make the big difference in the overall process.
Lastly and most importantly, the warm up is a great opportunity to zone out from all of the distractions you have had through out the day and focus on the session to come, because to get the most out of each session you need to give it your full attention so take the time to disconnect from the rest of the world and focus on the goal at hand.