Putting points into each of the talents trees will generally improve that trees area of expertise. A hunter that puts most of their points in Marksman will have much better ranged damage than a hunter that puts points Beast Mastery. But a hunter that puts points in Beast Mastery will have much better solo ability than a hunter with points in Marksman. Because some talents are not worth getting putting some of your points in other trees will make you more powerful and more well rounded. Putting every last one of your points in Marksman would increase your DPS. But if you took some points out of weak talents like Improved Arcane Shot and put them into BM talents like Improved Aspect of the Hawk or Survival Talents like Hawk Eye your DPS would go up. While many people try to go as far down into a tree as they can there is also a balancing game of going as deeply as you can into the other trees. This juggling of talents has led to the rise of Builds. Tested patterns of talents that players have found are the most effective at increasing one or more styles of play. But in the end, the skill of the player determines a characters success more then their build.

Beast Master Builds
Basic BM Build.
This is your Core beast master build. It covers all of the basics and allows some other useful abilities in the other trees so you can do small group activities.

Soloist BM Build.
This is designed for those who plan to spend most of their time alone. If you are going to do lots of farming, leveling or grinding this is probably the best.

PVP BM Build.
This is designed specifically for those who want to PVP as a beast master. The core of this build is balancing your pets DPS with your own, and using Bestial Wrath and Beast Within.

Marksmanship Builds
Basic MM Build.
This is a bare bones Marksmanship build. Primarily used in PVE encounters. But able to solo very effectively and PVP a bit as well.

Cookie Cutter PVE Build.
This is designed for raids and instances, but that is about it. It very little defense and uses up a lot of mana. But has some of the highest DPS a hunter can get.

Survivalist PVP Build.
This is designed for group PVP in battlegrounds and Arenas. It requires a lot of coordination though since it is a bare bones Marksmanship build. The extra points in survival are designed to help when you come into melee range.

Survival Builds
Small Scale PVE build.
This build is mainly used for CC in five man instances and ten man raids. It has lower DPS than other builds, but provides more overall utility and survivability.

Hinderer PVP build.
This is the standard Survival PVP build. It focuses on hindering the enemy with traps and keeping yourself alive as long as possible. While it is very hard for an enemy to kill you, it doesn't have very good offensive abilities compared to other trees.

Trapmaster Build.
This is a very limited build. It is excellent for kiting in PVE and PVP, focusing heavily on traps and hindering abilities. While it is not a useful build in many other situations, I find it very fun when I want to torment others in world PVP.