Why perform an engine swap?

Let's get the obvious reason out of the way.  Most of those who want to do the engine swap want power. 

It's a matter of how much power and how it will be used.  My car is still a daily driver but I would like to have to do some spirited driving and continue participating in autocross events and eventually try a bit of drag racing to see where the car measures up.  I like to tinker around with stuff but considering that this will be my first swap I consider this to be a serious challenge.  Performing this swap will not only make the car more fun to drive but give me a satisfaction of doing something other than bolt-ons all day.  From reading all the posts and researching sites and books on Celica engine swapping, I've come to several forks in the road.  To keep things simpler, I've limited the swap to only Toyota inline 4 engines.  I've heard stuff of legends where a V8 and a v6 have been swapped into 5th gens but I would most likely perform the less difficult of the swaps - great and original feats.  You'll hear from everyone that every swap is different.  Even with a Inline-4 engine, the kind of car you have and the type of engine you select will determine how much troubleshooting and wiring you will have to endure.

Depending on which route I decide to take

Excellent 3SGTE Swap Engine Articles
http://www.topshelfracing.com/project/main.htm
http://www.toyotacelicaonline.com/celica1/3sgteswap.htm

4AGE Swap (More of an Overview than it is in actual article)
http://www.geocities.com/celicasleeper/

For those who are interested in learning about the v6 swap or the V8:

Do a google search on Celica V6 Swap