For a long time, I used what is effectively known as a "bro-split". A bro-split is breaking up your workouts into specific body parts for specific days. It might look like:
Wednesday: Legs (aka: more chest and some biceps)
Every day: abs
While this can be effective for many people, there are a few major negatives.
First, to hit every body part you need to be able to commit at least five days per week to the gym. This worked well for me until kids and "real life" came along. For most people, committing five hours per week to the gym is not realistic. Between work, family and other commitments, it's simply not doable.
The second problem is that frequency is low. If you blast your chest on Monday, and then wait until the following Monday to blast it again, you're missing out on practicing the movements. Your muscle groups should be ready to go again between 48-72 hours after you've worked them. If you're only working them once per week, you're missing out on results.
Next, some days are not as enjoyable and get skipped. Some (most) people hate working out legs. Despite the fact that your lower body makes up half of your total body, it often gets neglected. For others, it might be shoulders, and I've even heard rumors that somewhere in the universe there are even some people who don't like working out their arms.
Finally, bro-splits encourage low-quality work. If you are following a properly programmed workout routine, you should be starting with the heaviest compound lifts. These moves will allow you to lift the most weight and give you the most bang for your buck. On a bro-split, you might start your leg day with squats, followed by leg extensions, some hamstring curls and finally some calf-raises. The problem is that after heavy squats, you start to accumulate "junk volume" - it's work that's not really doing much. You can't possibly load the other exercises enough to get the most out of them. Now, if you're a bodybuilder, it may be worth it, but for the average person, you're probably better off spending your time on big movements.
Full-body workouts address all of these issues.
First, you can get great results by working out 2-3 times per week. With full-body workouts, you don't need to carve out the same amount of time as you do with bro-splits. When you workout the entire body each time, you can get away with 2-3 hours per week of exercising.
Next, frequency is high. I like to think of exercises as a skill. A basketball player is far better off shooting 100 shots each day of the week than 700 shots one day and taking the next six off. Same with working out. The exercises you do are skills you are trying to develop. Instead of doing all of your bench pressing one day, spreading it out to 2-3 days gives you better practice.
Third, full-body workouts give you a carrot to dangle. I often neglected leg day because it wasn't enjoyable. However, with full-body workouts, my sets of squats are followed by upper-body training. It's the equivalent of eating your vegetables before dessert.
Finally, when you are only doing one set per body part, it forces you to use the best exercises. You will get far more out of bench pressing 2-3 times per week than you will throwing in some chest flyes. Full body workouts often revolve around heavy compound movements (squats, deadlifts, bench press, overhead press and chin-ups).
Now, there are some negatives to full-body workouts as well.
The biggest negative to full-body workouts is the time factor. When I do a bro-split type workout, I can often finish in 30-45 minutes. A full-body workout consistently takes around an hour, maybe a bit more. Some people may prefer to workout more frequently for shorter sessions, while others may like the less-freuqent-but-longer workouts.
So to put it all together, here is a very simple, yet effective full-body workout that you may want to try:
Squat 2-3 sets of 4-6 reps
Bench Press 2-3 sets of 4-6 reps
Rows (or chin-ups) 2-3 sets of 6-8reps
Curls 2-3 sets of 8-10 reps
Deadlift 2-3 sets of 4-6 reps
Overhead Press 2-3 sets of 4-6 reps
Tricep Pushdowns 2-3 sets of 8-10 reps
Cable Crunches 2-3 sets of 8-10 reps
*rest 2-3 minutes between sets of 4-6 reps and 1-2 minutes between sets of 6-10 reps.
These workouts would be alternated 2-3 times per week (AB, AB, OR ABA, BAB). Each day you get some work for your push muscles (bench press, overhead press, tricep pushdowns), pull muscles (rows/chin-ups, curls, deadlift) and legs (squats, deadlift). By adding some direct core work on Workout B, you round everything out.
If you were working out from home and you have limited equipment, you could try something like this:
Single leg-Squat variation 2-3 sets of 4-6 reps
Push-up variation 2-3 sets of 4-6 reps
Chin-up/Inverted Row 2-3 sets of 6-8reps
Curls 2-3 sets of 8-10 reps
Single leg Deadlift 2-3 sets of 4-6 reps
Handstand push-up variation 2-3 sets of 4-6 reps
Chair Dips 2-3 sets of 8-10 reps
Pilates Roll-ups 2-3 sets of 8-10 reps
These moves mimic the gym movements, but require minimal equipment. A chin-up bar, some soup cans or some resistance bands would be more than enough to make this work. Variations of the movements can be found with a quick YouTube search.