The Logic Behind Distribution
Linux is really the name of the kernel, when combined with the packages around it they are commonly referred to as a distribution, or distro for short.
Why the distro exists
A distro has a mission to fulfil, that is to provide access to a set of packages, which allow the user get a selection suitable packages which have interdependencies resolved so they all work nicely together. [Or you end up in dependency hell.]
Why not bring in software from outside
This is not done on a general basis, because the software that is working together may not be able to cope with some of the requirements, it may in fact clash with the working system causing a critical package to become non functioning.
The first thing you should ask yourself is what functionality is in this package that can't be obtained from another package in the distro.
There are usually several packages that can be used to achieve a single job. Example - maybe you want to use something else for email other than evolution, so you might go for thunderbird or mutt depending on your circumstances.
When a distro is set up it generally has a support period, when that period is over then the support may disappear. Typically what happens during that support phase is a few packages have security issues, these issues get fixed and then an announcement is made that there is a new version of the software available. In some extreme cases the software actually gets upgraded but this is not the norm.
Implications of this Security patching
You do not need to install the latest version when something goes wrong because it is taken care of within your distro. This means that you have "stability" and the packages should stay the same and everything on the system continues to work after the fix.
If you still want to bring in outside software
Warning: Remember the dependency hell is only one program away unless you are very sure of what you are doing.
If you are going to bring in something that is not in your version of your distro consider have you got all sources, http://wiki.ubuntu.com/AddingRepositoriesHowto, if you do then you should consider source packages before using something like Alien, or debs from Debian, taking sources not from your version of your distro may lead to a broken system. If you decide that the package you want is not in the repositories listed above, you might need to compile the package from a tar.gz. Before going off and compiling the tar.gz please read https://wiki.ubuntu.com/CompilingSoftware and http://wiki.ubuntu.com/CheckInstall for more information on compiling software.
Implications of this choice
You get to manage the application and its security threats and if you install 10 or 15 you will be seriously increasing your management overhead on the system, because you can't have one thing breaking another. To counteract this you need to have moderate to good programming skills.
What to do
Make your choice in full knowledge of your options. Always think do I have to, what will happen if it breaks.
Backup your system before you go changing things.