When to use /Users/m/bin instead of /usr/local/bin (& whats the diff?)?

Q1. I understand that /usr/local/bin means I can install/uninstall stuff in here and have any chance of messing up my original system files or effecting any other users. I created this directory myself.

But what about the directory I didn't create, namely /Users/m/bin? How is that directory different and when should I use one over the other?

mbp:~ m$ ls /usr/local/bin
brew               createuser         ecpg                git-shell          initdb             pg_controldata      pg_resetxlog       pgbench            reindexdb          vacuumlo
clusterdb          dropdb             git                 git-upload-archive oid2name           pg_ctl             pg_restore          postgres           uuid
createdb           droplang           git-cvsserver      git-upload-pack     pg_archivecleanup  pg_dump            pg_standby         postmaster          uuid-config
createlang         dropuser           git-receive-pack   gitk                pg_config          pg_dumpall         pg_upgrade         psql                vacuumdb
mbp:~ m$ ls /Users/m/bin
mate          rvm           rvm-auto-ruby rvm-exec      rvm-installer rvm-prompt    rvm-shell     rvmsudo

Q2. Since "mate" (ie textmate) is not found when I try execute it, should I amend my .profile file to export PATH=/usr/local/bin:/Users/m/bin:$PATH? ...but in fact this is what got me asking question 1. That is, whats the use of this directory if I already have /usr/local/bin, shouldn't I have all this local bin stuff in one place rather?

mbp:~ m$ mate
 -bash: mate: command not found
mbp:~ m$ cat ~/.profile 
# NOTE: to reload this file: "source ~/.profile"
export PATH=/usr/local/bin:$PATH

# ALIASES 
ENV=~/.env
export ENV
. $ENV

# Load RVM into your shell sessions as a function (see http://beginrescueend.com/rvm/install/)
[[ -s "$HOME/.rvm/scripts/rvm" ]] && . "$HOME/.rvm/scripts/rvm" # Load RVM function

mbp:~ m$ echo $PATH
/Users/m/.rvm/gems/ruby-1.9.2-p180/bin:/Users/m/.rvm/gems/ruby-1.9.2-p180@global/bin:/Users/m/.rvm/rubies/ruby-1.9.2-p180/bin:
/Users/m/.rvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin

Thanks, Michelle

1-) I m not sure but Mac OS X does not include /usr/local/bin in its default PATH.
More information you can look these about local bin folders
https://discussions.apple.com/message/1831793
https://discussions.apple.com/thread/2400512

2-) Yes you can add this path(your $HOME variable to your profile files.
I guess ruby(+rvm) installed ~/bin directory as default but you can install it to different directory if you has w permission (i.e /usr/local/bin and must add it to PATH variable in profile files (/etc/profile , ~/.bashrc|.bash_profile|.bash_login....)

regards
ygemici