This is more of a generic question, based on trying out Window Managers like Awesome, Mate and others.
To me looks like that other Window Managers like Gnome3 and/or Unity are heavy and pointless.

I do understand that having all the composed UIs is more pleasant for the eye, but apart that, what are the other major benefits?
To make an example, when I run the game Heroes of Newerth (using nVidia drivers) under:

• Unity : the FPS drops sharply
• Gnome3 : FPS is ok, but X and other processes use 15~20% of CPU and quite some additional memory
• Awesome : FPS is ok, and other processes use very little memory and CPU

Below some numbers regarding what I'm saying (please note my system is 64 bit, AMD Phenom II X4, 8 GB RAM, nd nVidia 470 GTX, SSD disk). All data is sorted by mem usage (watch -d -n 10 "ps -e -o pcpu,pmem,pid,user,cmd --sort=-pmem | head -20"); again note that CPU time of ./hon-x86_64 might be different due to the fact I can't take the snapshot of the system during exactly same time.

Awesome:

%CPU %MEM   PID USER     CMD
91.8 21.6  3579 ema      ./hon-x86_64
 2.4  0.9  3223 root     /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
 1.6  0.4  2600 ema      /usr/lib/erlang/erts-5.8.5/bin/beam.smp -Bd -K true -A 4 -- -root /usr/lib/erlang -progname erl -- -home /home/ema -- -noshell -noinp
 0.3  0.2  3602 ema      gnome-terminal
 0.0  0.2  2698 ema      /usr/bin/python /usr/lib/desktopcouch/desktopcouch-service

Gnome3:

%CPU %MEM   PID USER     CMD
82.7 21.0  5528 ema      ./hon-x86_64
17.7  1.7  5315 ema      /usr/bin/gnome-shell
 5.8  1.2  5062 root     /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
 1.0  0.4  5657 ema      /usr/bin/python /usr/lib/ubuntuone-client/ubuntuone-syncdaemon
 0.7  0.3  5331 ema      nautilus -n                                                                                                            
 1.6  0.3  2600 ema      /usr/lib/erlang/erts-5.8.5/bin/beam.smp -Bd -K true -A 4 -- -root /usr/lib/erlang -progname erl -- -home /home/ema -- -
 0.9  0.2  5451 ema      gnome-terminal
 0.1  0.2  5400 ema      /usr/bin/python /usr/lib/desktopcouch/desktopcouch-service

Unity 3D:

%CPU %MEM   PID USER     CMD
87.2 21.1  6554 ema      ./hon-x86_64
10.7  2.6  6105 ema      compiz
17.8  1.1  5842 root     /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
 1.3  0.9  6672 root     /usr/bin/python /usr/sbin/aptd
 0.4  0.4  6606 ema      /usr/bin/python /usr/lib/ubuntuone-client/ubuntuone-syncdaemon
 0.5  0.3  6115 ema      nautilus -n                                                                                                                                       
 1.5  0.3  2600 ema      /usr/lib/erlang/erts-5.8.5/bin/beam.smp -Bd -K true -A 4 -- -root /usr/lib/erlang -progname erl -- -home /home/ema -- -noshell -noinput -sasl errl
 0.3  0.2  6180 ema      /usr/lib/unity/unity-panel-service

So my point is, what's the rationale behind going towards such heavy WMs/Composers?