I came accross a great article by Regan Wald, in which he describes how "software is not made of bricks". This is something I agree with totally, as many non-programmers often have the outlook on programming in a way that it is simply like slotting lego together. It's not without reason either, most media outlets (movies, TV) portray it in exactly this way. This is aimed at non-programming types trying to plan projects or manage a team of programmers.

Programming is not particularly "proceedural" by nature. It's very very unusual that a programmer can simply "slot" in functionality for a specific feature without needing lots of ground work for it. Lets say you have some software which provides some accounting functionality, it's quite easy to assume "hey we have an accounting brick now, lets just slot that on top of our completely seperate ordering system". You -may- save some time by being able to re-use a chunk of code, but at the end of the day, refactoring old code will probably take up any time saved in that regard. Problem solving and thinking may be reduced however.

Just be careful not to fall into the trap of thinking that porting code accross from totally unrelated projects is a simple snap-out snap-in task, because 99% of the time it will take almost as long as it did the first time.