How to determine the end of words?
Today over at LanguageLog, I came across this sentence:

台灣經驗不僅是對其他開發中國家的一種啟發，更是台灣免於赤化的最佳保障。

Inadvertently, when scanning that phrase I ran down a gardenpath (yes, that's what linguists call it: a fruitless attempt that turns out to be the wrong choice, so you have to back up). Turns out it's not 開發　中國(家) *"develop China's (state)??", but, rather, 開發中　國家 "in-development states" (i.e. "developing countries"). 

Such things will happen and happen again to the reader, and if you care to know more, head over to said site and google it for 'gardenpaths', there's lots of examples for a number of languages. Just the other day I realized German "Maisturm" is ambiguous: is it "Mais-Turm" (maize/corn tower) or "Mai-Sturm" (May tempest)? Probably the latter in most cases, but only context can tell. 

I remember some of the beginner's textbooks for Chinese using spaces between words, so I guess you'll still be able to find some. As for why spaces are not normally used in Chinese and Japanese (but in Korean), one can only guess that people find them too unsightly, not really needed and maybe too big a change from what they're used to. 

Also, while extra spaces might benefit the reader, they do put a burden on the writer (try to add them while staying consistent—it's not easy!).