This is because the space is treated as a word separator. The standard punctuation marks are also word separators and provide differing degrees of pause between words. This can increase the speed of execution if you fill some string variables at the start of your program, and then use them when you wish to speak. You can then separate the initial sounds of each word, and use these to create your own vocabulary. This is an area for experimentation.
SIZE returns the amount of free memory.
In addition, the cassette loader cannot handle programs over 12k. This function is useful if your program contains a lot of lines either the same or with only small differences. It does require a little more care in use, but gives you considerably more programming power. An added attraction of the module is that it permits you to load and run Assembly language programs, provided you have the extra peripherals required. You require a disk system and the 32k memory expansion.